﻿<?xml version="1.0" encoding="utf-8" standalone="yes"?><rss version="2.0" xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:trackback="http://madskills.com/public/xml/rss/module/trackback/" xmlns:wfw="http://wellformedweb.org/CommentAPI/" xmlns:slash="http://purl.org/rss/1.0/modules/slash/"><channel><title>C++博客-λ-calculus（惊愕到手了欧耶，GetBlogPostIds.aspx）-随笔分类-C++实用技巧</title><link>http://www.cppblog.com/vczh/category/14099.html</link><description>【QQ：343056143】【Email：vczh@163.com】【新浪微博：http://weibo.com/vczh】</description><language>zh-cn</language><lastBuildDate>Fri, 28 Feb 2014 21:35:18 GMT</lastBuildDate><pubDate>Fri, 28 Feb 2014 21:35:18 GMT</pubDate><ttl>60</ttl><item><title>随手撸了一个可以写递归lambda的Y函数</title><link>http://www.cppblog.com/vczh/archive/2014/03/01/205998.html</link><dc:creator>陈梓瀚(vczh)</dc:creator><author>陈梓瀚(vczh)</author><pubDate>Fri, 28 Feb 2014 16:34:00 GMT</pubDate><guid>http://www.cppblog.com/vczh/archive/2014/03/01/205998.html</guid><wfw:comment>http://www.cppblog.com/vczh/comments/205998.html</wfw:comment><comments>http://www.cppblog.com/vczh/archive/2014/03/01/205998.html#Feedback</comments><slash:comments>1</slash:comments><wfw:commentRss>http://www.cppblog.com/vczh/comments/commentRss/205998.html</wfw:commentRss><trackback:ping>http://www.cppblog.com/vczh/services/trackbacks/205998.html</trackback:ping><description><![CDATA[<p>最近学习C++11的variadic template argument，终于可以摆脱用fpmacro模板来复制一大堆代码的做法了，好开心。这个例子的main函数用lambda写了一个斐波那契数列的递归计算函数。跟以往不同的是，在Y函数的帮助下，这个lambda表达是可以成功看到自己，然后递归调用。当然这仍然需要用普通的C++递归来实现，并不是λ-calculus那个高大上的Y Combinator。
</p><p>
 </p><p><span style="color:blue"><span style="font-family:Consolas; font-size:9pt; background-color:white">#include<span style="color:black">
					<span style="color:#a31515">&lt;functional&gt;</span></span></span>
		</span></p><p><span style="color:blue; font-family:Consolas; font-size:9pt; background-color:white">#include<span style="color:black">
				<span style="color:#a31515">&lt;memory&gt;<span style="color:black">
					</span></span></span></span></p><p><span style="color:blue; font-family:Consolas; font-size:9pt; background-color:white">#include<span style="color:black">
				<span style="color:#a31515">&lt;iostream&gt;<span style="color:black">
					</span></span></span></span></p><p><span style="color:blue; font-family:Consolas; font-size:9pt; background-color:white">#include<span style="color:black">
				<span style="color:#a31515">&lt;string&gt;<span style="color:black">
					</span></span></span></span></p><p>
 </p><p><span style="color:blue; font-family:Consolas; font-size:9pt; background-color:white">using<span style="color:black">
				<span style="color:blue">namespace<span style="color:black"> std;
</span></span></span></span></p><p>
 </p><p><span style="color:blue; font-family:Consolas; font-size:9pt; background-color:white">template<span style="color:black">&lt;<span style="color:blue">typename<span style="color:black">
						<span style="color:#2b91af">TResult<span style="color:black">, <span style="color:blue">typename<span style="color:black"> ...<span style="color:#2b91af">TArgs<span style="color:black">&gt;
</span></span></span></span></span></span></span></span></span></span></p><p><span style="color:blue; font-family:Consolas; font-size:9pt; background-color:white">class<span style="color:black">
				<span style="color:#2b91af">YBuilder<span style="color:black">
					</span></span></span></span></p><p><span style="color:black; font-family:Consolas; font-size:9pt; background-color:white">{
</span></p><p><span style="color:blue; font-family:Consolas; font-size:9pt; background-color:white">private<span style="color:black">:
</span></span></p><p><span style="color:black; font-family:Consolas; font-size:9pt; background-color:white">    <span style="color:#2b91af">function<span style="color:black">&lt;<span style="color:#2b91af">TResult<span style="color:black">(<span style="color:#2b91af">function<span style="color:black">&lt;<span style="color:#2b91af">TResult<span style="color:black">(<span style="color:#2b91af">TArgs<span style="color:black">...)&gt;, <span style="color:#2b91af">TArgs<span style="color:black">...)&gt; partialLambda;
</span></span></span></span></span></span></span></span></span></span></span></span></span></p><p>
 </p><p><span style="color:blue; font-family:Consolas; font-size:9pt; background-color:white">public<span style="color:black">:
</span></span></p><p><span style="color:black; font-family:Consolas; font-size:9pt; background-color:white">    YBuilder(<span style="color:#2b91af">function<span style="color:black">&lt;<span style="color:#2b91af">TResult<span style="color:black">(<span style="color:#2b91af">function<span style="color:black">&lt;<span style="color:#2b91af">TResult<span style="color:black">(<span style="color:#2b91af">TArgs<span style="color:black">...)&gt;, <span style="color:#2b91af">TArgs<span style="color:black">...)&gt; <span style="color:gray">_partialLambda<span style="color:black">)
</span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></p><p><span style="color:black; font-family:Consolas; font-size:9pt; background-color:white">        :partialLambda(<span style="color:gray">_partialLambda<span style="color:black">)
</span></span></span></p><p><span style="color:black; font-family:Consolas; font-size:9pt; background-color:white">    {
</span></p><p><span style="color:black; font-family:Consolas; font-size:9pt; background-color:white">    }
</span></p><p>
 </p><p><span style="color:black; font-family:Consolas; font-size:9pt; background-color:white">    <span style="color:#2b91af">TResult<span style="color:black"> operator()(<span style="color:#2b91af">TArgs<span style="color:black"> ...<span style="color:gray">args<span style="color:black">)<span style="color:blue">const<span style="color:black">
										</span></span></span></span></span></span></span></span></span></p><p><span style="color:black; font-family:Consolas; font-size:9pt; background-color:white">    {
</span></p><p><span style="color:black; font-family:Consolas; font-size:9pt; background-color:white">        <span style="color:blue">return<span style="color:black"> partialLambda(
</span></span></span></p><p><span style="color:black; font-family:Consolas; font-size:9pt; background-color:white">            [<span style="color:blue">this<span style="color:black">](<span style="color:#2b91af">TArgs<span style="color:black"> ...<span style="color:gray">args<span style="color:black">)
</span></span></span></span></span></span></span></p><p><span style="color:black; font-family:Consolas; font-size:9pt; background-color:white">            {
</span></p><p><span style="color:black; font-family:Consolas; font-size:9pt; background-color:white">                <span style="color:blue">return<span style="color:black">
					<span style="color:blue">this<span style="color:black">-&gt;<span style="color:blue">operator<span style="color:black">()(<span style="color:gray">args<span style="color:black">...);
</span></span></span></span></span></span></span></span></span></p><p><span style="color:black; font-family:Consolas; font-size:9pt; background-color:white">            }, <span style="color:gray">args<span style="color:black">...);
</span></span></span></p><p><span style="color:black; font-family:Consolas; font-size:9pt; background-color:white">    }
</span></p><p><span style="color:black; font-family:Consolas; font-size:9pt; background-color:white">};
</span></p><p>
 </p><p><span style="color:blue; font-family:Consolas; font-size:9pt; background-color:white">template<span style="color:black">&lt;<span style="color:blue">typename<span style="color:black">
						<span style="color:#2b91af">TMethod<span style="color:black">&gt;
</span></span></span></span></span></span></p><p><span style="color:blue; font-family:Consolas; font-size:9pt; background-color:white">struct<span style="color:black">
				<span style="color:#2b91af">PartialLambdaTypeRetriver<span style="color:black">
					</span></span></span></span></p><p><span style="color:black; font-family:Consolas; font-size:9pt; background-color:white">{
</span></p><p><span style="color:black; font-family:Consolas; font-size:9pt; background-color:white">    <span style="color:blue">typedef<span style="color:black">
					<span style="color:blue">void<span style="color:black">
							<span style="color:#2b91af">FunctionType<span style="color:black">;
</span></span></span></span></span></span></span></p><p><span style="color:black; font-family:Consolas; font-size:9pt; background-color:white">    <span style="color:blue">typedef<span style="color:black">
					<span style="color:blue">void<span style="color:black">
							<span style="color:#2b91af">LambdaType<span style="color:black">;
</span></span></span></span></span></span></span></p><p><span style="color:black; font-family:Consolas; font-size:9pt; background-color:white">    <span style="color:blue">typedef<span style="color:black">
					<span style="color:blue">void<span style="color:black">
							<span style="color:#2b91af">YBuilderType<span style="color:black">;
</span></span></span></span></span></span></span></p><p><span style="color:black; font-family:Consolas; font-size:9pt; background-color:white">};
</span></p><p>
 </p><p><span style="color:blue; font-family:Consolas; font-size:9pt; background-color:white">template<span style="color:black">&lt;<span style="color:blue">typename<span style="color:black">
						<span style="color:#2b91af">TClass<span style="color:black">, <span style="color:blue">typename<span style="color:black">
										<span style="color:#2b91af">TResult<span style="color:black">, <span style="color:blue">typename<span style="color:black"> ...<span style="color:#2b91af">TArgs<span style="color:black">&gt;
</span></span></span></span></span></span></span></span></span></span></span></span></span></span></p><p><span style="color:blue; font-family:Consolas; font-size:9pt; background-color:white">struct<span style="color:black">
				<span style="color:#2b91af">PartialLambdaTypeRetriver<span style="color:black">&lt;<span style="color:#2b91af">TResult<span style="color:black">(<span style="color:blue">__thiscall<span style="color:black">
										<span style="color:#2b91af">TClass<span style="color:black">::*)(<span style="color:#2b91af">function<span style="color:black">&lt;<span style="color:#2b91af">TResult<span style="color:black">(<span style="color:#2b91af">TArgs<span style="color:black">...)&gt;, <span style="color:#2b91af">TArgs<span style="color:black">...)&gt;
</span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></p><p><span style="color:black; font-family:Consolas; font-size:9pt; background-color:white">{
</span></p><p><span style="color:black; font-family:Consolas; font-size:9pt; background-color:white">    <span style="color:blue">typedef<span style="color:black">
					<span style="color:#2b91af">TResult<span style="color:black">
							<span style="color:#2b91af">FunctionType<span style="color:black">(<span style="color:#2b91af">TArgs<span style="color:black">...);
</span></span></span></span></span></span></span></span></span></p><p><span style="color:black; font-family:Consolas; font-size:9pt; background-color:white">    <span style="color:blue">typedef<span style="color:black">
					<span style="color:#2b91af">TResult<span style="color:black">
							<span style="color:#2b91af">LambdaType<span style="color:black">(<span style="color:#2b91af">function<span style="color:black">&lt;<span style="color:#2b91af">TResult<span style="color:black">(<span style="color:#2b91af">TArgs<span style="color:black">...)&gt;, <span style="color:#2b91af">TArgs<span style="color:black">...);
</span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></p><p><span style="color:black; font-family:Consolas; font-size:9pt; background-color:white">    <span style="color:blue">typedef<span style="color:black">
					<span style="color:#2b91af">YBuilder<span style="color:black">&lt;<span style="color:#2b91af">TResult<span style="color:black">, <span style="color:#2b91af">TArgs<span style="color:black">...&gt; <span style="color:#2b91af">YBuilderType<span style="color:black">;
</span></span></span></span></span></span></span></span></span></span></span></p><p><span style="color:black; font-family:Consolas; font-size:9pt; background-color:white">};
</span></p><p>
 </p><p><span style="color:blue; font-family:Consolas; font-size:9pt; background-color:white">template<span style="color:black">&lt;<span style="color:blue">typename<span style="color:black">
						<span style="color:#2b91af">TClass<span style="color:black">, <span style="color:blue">typename<span style="color:black">
										<span style="color:#2b91af">TResult<span style="color:black">, <span style="color:blue">typename<span style="color:black"> ...<span style="color:#2b91af">TArgs<span style="color:black">&gt;
</span></span></span></span></span></span></span></span></span></span></span></span></span></span></p><p><span style="color:blue; font-family:Consolas; font-size:9pt; background-color:white">struct<span style="color:black">
				<span style="color:#2b91af">PartialLambdaTypeRetriver<span style="color:black">&lt;<span style="color:#2b91af">TResult<span style="color:black">(<span style="color:blue">__thiscall<span style="color:black">
										<span style="color:#2b91af">TClass<span style="color:black">::*)(<span style="color:#2b91af">function<span style="color:black">&lt;<span style="color:#2b91af">TResult<span style="color:black">(<span style="color:#2b91af">TArgs<span style="color:black">...)&gt;, <span style="color:#2b91af">TArgs<span style="color:black">...)<span style="color:blue">const<span style="color:black">&gt;
</span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></p><p><span style="color:black; font-family:Consolas; font-size:9pt; background-color:white">{
</span></p><p><span style="color:black; font-family:Consolas; font-size:9pt; background-color:white">    <span style="color:blue">typedef<span style="color:black">
					<span style="color:#2b91af">TResult<span style="color:black">
							<span style="color:#2b91af">FunctionType<span style="color:black">(<span style="color:#2b91af">TArgs<span style="color:black">...);
</span></span></span></span></span></span></span></span></span></p><p><span style="color:black; font-family:Consolas; font-size:9pt; background-color:white">    <span style="color:blue">typedef<span style="color:black">
					<span style="color:#2b91af">TResult<span style="color:black">
							<span style="color:#2b91af">LambdaType<span style="color:black">(<span style="color:#2b91af">function<span style="color:black">&lt;<span style="color:#2b91af">TResult<span style="color:black">(<span style="color:#2b91af">TArgs<span style="color:black">...)&gt;, <span style="color:#2b91af">TArgs<span style="color:black">...);
</span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></p><p><span style="color:black; font-family:Consolas; font-size:9pt; background-color:white">    <span style="color:blue">typedef<span style="color:black">
					<span style="color:#2b91af">YBuilder<span style="color:black">&lt;<span style="color:#2b91af">TResult<span style="color:black">, <span style="color:#2b91af">TArgs<span style="color:black">...&gt; <span style="color:#2b91af">YBuilderType<span style="color:black">;
</span></span></span></span></span></span></span></span></span></span></span></p><p><span style="color:black; font-family:Consolas; font-size:9pt; background-color:white">};
</span></p><p>
 </p><p><span style="color:blue; font-family:Consolas; font-size:9pt; background-color:white">template<span style="color:black">&lt;<span style="color:blue">typename<span style="color:black">
						<span style="color:#2b91af">TLambda<span style="color:black">&gt;
</span></span></span></span></span></span></p><p><span style="color:#2b91af; font-family:Consolas; font-size:9pt; background-color:white">function<span style="color:black">&lt;<span style="color:blue">typename<span style="color:black">
						<span style="color:#2b91af">PartialLambdaTypeRetriver<span style="color:black">&lt;<span style="color:blue">decltype<span style="color:black">(&amp;<span style="color:#2b91af">TLambda<span style="color:black">::<span style="color:blue">operator<span style="color:black">())&gt;::<span style="color:#2b91af">FunctionType<span style="color:black">&gt; Y(<span style="color:#2b91af">TLambda<span style="color:black">
																		<span style="color:gray">partialLambda<span style="color:black">)
</span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></p><p><span style="color:black; font-family:Consolas; font-size:9pt; background-color:white">{
</span></p><p><span style="color:black; font-family:Consolas; font-size:9pt; background-color:white">    <span style="color:blue">return<span style="color:black">
					<span style="color:blue">typename<span style="color:black">
							<span style="color:#2b91af">PartialLambdaTypeRetriver<span style="color:black">&lt;<span style="color:blue">decltype<span style="color:black">(&amp;<span style="color:#2b91af">TLambda<span style="color:black">::<span style="color:blue">operator<span style="color:black">())&gt;::<span style="color:#2b91af">YBuilderType<span style="color:black">(<span style="color:gray">partialLambda<span style="color:black">);
</span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></p><p><span style="color:black; font-family:Consolas; font-size:9pt; background-color:white">}
</span></p><p>
 </p><p><span style="color:blue; font-family:Consolas; font-size:9pt; background-color:white">int<span style="color:black">
				<span style="color:#6f008a">_tmain<span style="color:black">(<span style="color:blue">int<span style="color:black">
								<span style="color:gray">argc<span style="color:black">, <span style="color:#2b91af">_TCHAR<span style="color:black">* <span style="color:gray">argv<span style="color:black">[])
</span></span></span></span></span></span></span></span></span></span></span></span></p><p><span style="color:black; font-family:Consolas; font-size:9pt; background-color:white">{
</span></p><p><span style="color:black; font-family:Consolas; font-size:9pt; background-color:white">    <span style="color:blue">auto<span style="color:black"> fib = Y([](<span style="color:#2b91af">function<span style="color:black">&lt;<span style="color:blue">int<span style="color:black">(<span style="color:blue">int<span style="color:black">)&gt; <span style="color:gray">self<span style="color:black">, <span style="color:blue">int<span style="color:black">
															<span style="color:gray">index<span style="color:black">)
</span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></p><p><span style="color:black; font-family:Consolas; font-size:9pt; background-color:white">    {
</span></p><p><span style="color:black; font-family:Consolas; font-size:9pt; background-color:white">        <span style="color:blue">return<span style="color:black">
					<span style="color:gray">index<span style="color:black">&lt;2
</span></span></span></span></span></p><p><span style="color:black; font-family:Consolas; font-size:9pt; background-color:white">            ?1
</span></p><p><span style="color:black; font-family:Consolas; font-size:9pt; background-color:white">            :<span style="color:gray">self<span style="color:black">(<span style="color:gray">index<span style="color:black">-1)+<span style="color:gray">self<span style="color:black">(<span style="color:gray">index<span style="color:black">-2);
</span></span></span></span></span></span></span></span></span></p><p><span style="color:black; font-family:Consolas; font-size:9pt; background-color:white">    });
</span></p><p>
 </p><p><span style="color:black; font-family:Consolas; font-size:9pt; background-color:white">    <span style="color:blue">for<span style="color:black"> (<span style="color:blue">int<span style="color:black"> i = 0; i &lt; 10; i++)
</span></span></span></span></span></p><p><span style="color:black; font-family:Consolas; font-size:9pt; background-color:white">    {
</span></p><p><span style="color:black; font-family:Consolas; font-size:9pt; background-color:white">        cout &lt;&lt; fib(i) &lt;&lt; <span style="color:#a31515">" "<span style="color:black">;
</span></span></span></p><p><span style="color:black; font-family:Consolas; font-size:9pt; background-color:white">    }
</span></p><p><span style="color:black; font-family:Consolas; font-size:9pt; background-color:white">    cout &lt;&lt; endl;
</span></p><p><span style="color:black; font-family:Consolas; font-size:9pt; background-color:white">}</span><span style="font-size:1pt">
		</span></p><img src ="http://www.cppblog.com/vczh/aggbug/205998.html" width = "1" height = "1" /><br><br><div align=right><a style="text-decoration:none;" href="http://www.cppblog.com/vczh/" target="_blank">陈梓瀚(vczh)</a> 2014-03-01 00:34 <a href="http://www.cppblog.com/vczh/archive/2014/03/01/205998.html#Feedback" target="_blank" style="text-decoration:none;">发表评论</a></div>]]></description></item><item><title>C++实用技巧之配置Visual C++的调试器显示数据结构的格式（附Vczh Library++配置文件）</title><link>http://www.cppblog.com/vczh/archive/2013/03/21/198665.html</link><dc:creator>陈梓瀚(vczh)</dc:creator><author>陈梓瀚(vczh)</author><pubDate>Thu, 21 Mar 2013 03:55:00 GMT</pubDate><guid>http://www.cppblog.com/vczh/archive/2013/03/21/198665.html</guid><wfw:comment>http://www.cppblog.com/vczh/comments/198665.html</wfw:comment><comments>http://www.cppblog.com/vczh/archive/2013/03/21/198665.html#Feedback</comments><slash:comments>4</slash:comments><wfw:commentRss>http://www.cppblog.com/vczh/comments/commentRss/198665.html</wfw:commentRss><trackback:ping>http://www.cppblog.com/vczh/services/trackbacks/198665.html</trackback:ping><description><![CDATA[<p>今天我写了一个给Visual C++用的配置，用来让VC++在显示自己写的字符串和容器等设施变得跟显示STL一样漂亮。VC++的可配置型还是很高的，我们只要写一个xml，就可以改变调试器对自己的数据结构的显示了.</p>
<p>在这里我简单地介绍一下用法。假设大家觉得vlpp（Vczh Library++，也就是GacUI用的那个库）的WString啊List这些东西在调试器里面显示出来的东西太丑，就可以用以下三步来修改它。</p>
<p>1：去<a title="http://gac.codeplex.com/SourceControl/changeset/view/99419#2395529" href="http://gac.codeplex.com/SourceControl/changeset/view/99419#2395529">http://gac.codeplex.com/SourceControl/changeset/view/99419#2395529</a>下载我写的那个natvis文件。这个文件在整个zip包里面的位置是Common\vlpp.natvis<br />2：把这个文件复制到C:\Program Files (x86)\Microsoft Visual Studio 11.0\Common7\Packages\Debugger\Visualizers（如果使用默认安装路径的话）<br />3：重启你最喜爱的Visual Studio 2012，就可以看到下面的东西了：</p>
<p><a href="http://www.cppblog.com/images/cppblog_com/vczh/Windows-Live-Writer/51783bf28f3a_A413/image_2.png"><img style="background-image: none; border-bottom: 0px; border-left: 0px; padding-left: 0px; padding-right: 0px; display: inline; border-top: 0px; border-right: 0px; padding-top: 0px" title="image" border="0" alt="image" src="http://www.cppblog.com/images/cppblog_com/vczh/Windows-Live-Writer/51783bf28f3a_A413/image_thumb.png" width="275" height="95" /></a><br />空的智能指针</p>
<p><a href="http://www.cppblog.com/images/cppblog_com/vczh/Windows-Live-Writer/51783bf28f3a_A413/image_4.png"><img style="background-image: none; border-bottom: 0px; border-left: 0px; padding-left: 0px; padding-right: 0px; display: inline; border-top: 0px; border-right: 0px; padding-top: 0px" title="image" border="0" alt="image" src="http://www.cppblog.com/images/cppblog_com/vczh/Windows-Live-Writer/51783bf28f3a_A413/image_thumb_1.png" width="433" height="115" /></a><br />有东西的智能指针</p>
<p><a href="http://www.cppblog.com/images/cppblog_com/vczh/Windows-Live-Writer/51783bf28f3a_A413/image_6.png"><img style="background-image: none; border-bottom: 0px; border-left: 0px; padding-left: 0px; padding-right: 0px; display: inline; border-top: 0px; border-right: 0px; padding-top: 0px" title="image" border="0" alt="image" src="http://www.cppblog.com/images/cppblog_com/vczh/Windows-Live-Writer/51783bf28f3a_A413/image_thumb_2.png" width="224" height="64" /></a><br />有内容的&#8220;惰性计算&#8221;类</p>
<p><a href="http://www.cppblog.com/images/cppblog_com/vczh/Windows-Live-Writer/51783bf28f3a_A413/image_8.png"><img style="background-image: none; border-bottom: 0px; border-left: 0px; padding-left: 0px; padding-right: 0px; display: inline; border-top: 0px; border-right: 0px; padding-top: 0px" title="image" border="0" alt="image" src="http://www.cppblog.com/images/cppblog_com/vczh/Windows-Live-Writer/51783bf28f3a_A413/image_thumb_3.png" width="344" height="88" /></a><br />有内容但是还没计算的&#8220;惰性计算&#8221;类</p>
<p><a href="http://www.cppblog.com/images/cppblog_com/vczh/Windows-Live-Writer/51783bf28f3a_A413/image_10.png"><img style="background-image: none; border-bottom: 0px; border-left: 0px; padding-left: 0px; padding-right: 0px; display: inline; border-top: 0px; border-right: 0px; padding-top: 0px" title="image" border="0" alt="image" src="http://www.cppblog.com/images/cppblog_com/vczh/Windows-Live-Writer/51783bf28f3a_A413/image_thumb_4.png" width="353" height="83" /></a><br />没内容的&#8220;惰性计算&#8221;类</p>
<p><a href="http://www.cppblog.com/images/cppblog_com/vczh/Windows-Live-Writer/51783bf28f3a_A413/image_12.png"><img style="background-image: none; border-bottom: 0px; border-left: 0px; padding-left: 0px; padding-right: 0px; display: inline; border-top: 0px; border-right: 0px; padding-top: 0px" title="image" border="0" alt="image" src="http://www.cppblog.com/images/cppblog_com/vczh/Windows-Live-Writer/51783bf28f3a_A413/image_thumb_5.png" width="445" height="259" /></a><br />新鲜热辣的容器</p>
<p><a href="http://www.cppblog.com/images/cppblog_com/vczh/Windows-Live-Writer/51783bf28f3a_A413/image_14.png"><img style="background-image: none; border-bottom: 0px; border-left: 0px; padding-left: 0px; padding-right: 0px; display: inline; border-top: 0px; border-right: 0px; padding-top: 0px" title="image" border="0" alt="image" src="http://www.cppblog.com/images/cppblog_com/vczh/Windows-Live-Writer/51783bf28f3a_A413/image_thumb_6.png" width="667" height="226" /></a><br />新鲜热辣的映射</p>
<p><a href="http://www.cppblog.com/images/cppblog_com/vczh/Windows-Live-Writer/51783bf28f3a_A413/image_16.png"><img style="background-image: none; border-bottom: 0px; border-left: 0px; padding-left: 0px; padding-right: 0px; display: inline; border-top: 0px; border-right: 0px; padding-top: 0px" title="image" border="0" alt="image" src="http://www.cppblog.com/images/cppblog_com/vczh/Windows-Live-Writer/51783bf28f3a_A413/image_thumb_7.png" width="596" height="295" /></a><br />就连一对多的映射也是如此的新鲜热辣</p>
<p><a href="http://www.cppblog.com/images/cppblog_com/vczh/Windows-Live-Writer/51783bf28f3a_A413/image_18.png"><img style="background-image: none; border-bottom: 0px; border-left: 0px; padding-left: 0px; padding-right: 0px; display: inline; border-top: 0px; border-right: 0px; padding-top: 0px" title="image" border="0" alt="image" src="http://www.cppblog.com/images/cppblog_com/vczh/Windows-Live-Writer/51783bf28f3a_A413/image_thumb_8.png" width="318" height="161" /></a><br />List&lt;Nullable&lt;vint&gt;&gt;的互相嵌套也是如此的完美</p>
<p>如果大家想写自己的Customized Visualizer的话，可以去参考微软良心提供的文档<a title="http://msdn.microsoft.com/en-us/library/vstudio/jj620914.aspx" href="http://msdn.microsoft.com/en-us/library/vstudio/jj620914.aspx">http://msdn.microsoft.com/en-us/library/vstudio/jj620914.aspx</a>，然后按照上面的步骤写自己的natvis文件。在这里我把我的natvis贴上来，以供参考：</p>
<div style="border-bottom: #cccccc 1px solid; border-left: #cccccc 1px solid; padding-bottom: 5px; background-color: #f5f5f5; padding-left: 5px; padding-right: 5px; border-top: #cccccc 1px solid; border-right: #cccccc 1px solid; padding-top: 5px" class="cnblogs_code"><pre><span style="color: #0000ff">&lt;?</span><span style="color: #ff00ff">xml version="1.0" encoding="utf-8"</span><span style="color: #0000ff">?&gt;</span>
<span style="color: #0000ff">&lt;</span><span style="color: #800000">AutoVisualizer </span><span style="color: #ff0000">xmlns</span><span style="color: #0000ff">="http://schemas.microsoft.com/vstudio/debugger/natvis/2010"</span><span style="color: #0000ff">&gt;</span>

  <span style="color: #0000ff">&lt;</span><span style="color: #800000">Type </span><span style="color: #ff0000">Name</span><span style="color: #0000ff">="vl::ObjectString&amp;lt;wchar_t&amp;gt;"</span><span style="color: #0000ff">&gt;</span>
    <span style="color: #0000ff">&lt;</span><span style="color: #800000">DisplayString</span><span style="color: #0000ff">&gt;</span>{{ size={length}, buffer={buffer+start,su} }}<span style="color: #0000ff">&lt;/</span><span style="color: #800000">DisplayString</span><span style="color: #0000ff">&gt;</span>
    <span style="color: #0000ff">&lt;</span><span style="color: #800000">StringView</span><span style="color: #0000ff">&gt;</span>buffer+start,su<span style="color: #0000ff">&lt;/</span><span style="color: #800000">StringView</span><span style="color: #0000ff">&gt;</span>
    <span style="color: #0000ff">&lt;</span><span style="color: #800000">Expand</span><span style="color: #0000ff">&gt;</span>
      <span style="color: #0000ff">&lt;</span><span style="color: #800000">Item </span><span style="color: #ff0000">Name</span><span style="color: #0000ff">="[size]"</span><span style="color: #0000ff">&gt;</span>length<span style="color: #0000ff">&lt;/</span><span style="color: #800000">Item</span><span style="color: #0000ff">&gt;</span>
      <span style="color: #0000ff">&lt;</span><span style="color: #800000">ArrayItems</span><span style="color: #0000ff">&gt;</span>
        <span style="color: #0000ff">&lt;</span><span style="color: #800000">Size</span><span style="color: #0000ff">&gt;</span>length<span style="color: #0000ff">&lt;/</span><span style="color: #800000">Size</span><span style="color: #0000ff">&gt;</span>
        <span style="color: #0000ff">&lt;</span><span style="color: #800000">ValuePointer</span><span style="color: #0000ff">&gt;</span>buffer+start<span style="color: #0000ff">&lt;/</span><span style="color: #800000">ValuePointer</span><span style="color: #0000ff">&gt;</span>
      <span style="color: #0000ff">&lt;/</span><span style="color: #800000">ArrayItems</span><span style="color: #0000ff">&gt;</span>
    <span style="color: #0000ff">&lt;/</span><span style="color: #800000">Expand</span><span style="color: #0000ff">&gt;</span>
  <span style="color: #0000ff">&lt;/</span><span style="color: #800000">Type</span><span style="color: #0000ff">&gt;</span>

  <span style="color: #0000ff">&lt;</span><span style="color: #800000">Type </span><span style="color: #ff0000">Name</span><span style="color: #0000ff">="vl::ObjectString&amp;lt;char&amp;gt;"</span><span style="color: #0000ff">&gt;</span>
    <span style="color: #0000ff">&lt;</span><span style="color: #800000">DisplayString</span><span style="color: #0000ff">&gt;</span>{{ size={length}, buffer={buffer+start,s} }}<span style="color: #0000ff">&lt;/</span><span style="color: #800000">DisplayString</span><span style="color: #0000ff">&gt;</span>
    <span style="color: #0000ff">&lt;</span><span style="color: #800000">StringView</span><span style="color: #0000ff">&gt;</span>buffer+start,s<span style="color: #0000ff">&lt;/</span><span style="color: #800000">StringView</span><span style="color: #0000ff">&gt;</span>
    <span style="color: #0000ff">&lt;</span><span style="color: #800000">Expand</span><span style="color: #0000ff">&gt;</span>
      <span style="color: #0000ff">&lt;</span><span style="color: #800000">Item </span><span style="color: #ff0000">Name</span><span style="color: #0000ff">="[size]"</span><span style="color: #0000ff">&gt;</span>length<span style="color: #0000ff">&lt;/</span><span style="color: #800000">Item</span><span style="color: #0000ff">&gt;</span>
      <span style="color: #0000ff">&lt;</span><span style="color: #800000">ArrayItems</span><span style="color: #0000ff">&gt;</span>
        <span style="color: #0000ff">&lt;</span><span style="color: #800000">Size</span><span style="color: #0000ff">&gt;</span>length<span style="color: #0000ff">&lt;/</span><span style="color: #800000">Size</span><span style="color: #0000ff">&gt;</span>
        <span style="color: #0000ff">&lt;</span><span style="color: #800000">ValuePointer</span><span style="color: #0000ff">&gt;</span>buffer+start<span style="color: #0000ff">&lt;/</span><span style="color: #800000">ValuePointer</span><span style="color: #0000ff">&gt;</span>
      <span style="color: #0000ff">&lt;/</span><span style="color: #800000">ArrayItems</span><span style="color: #0000ff">&gt;</span>
    <span style="color: #0000ff">&lt;/</span><span style="color: #800000">Expand</span><span style="color: #0000ff">&gt;</span>
  <span style="color: #0000ff">&lt;/</span><span style="color: #800000">Type</span><span style="color: #0000ff">&gt;</span>

  <span style="color: #0000ff">&lt;</span><span style="color: #800000">Type </span><span style="color: #ff0000">Name</span><span style="color: #0000ff">="vl::collections::List&amp;lt;*,*&amp;gt;"</span><span style="color: #0000ff">&gt;</span>
    <span style="color: #0000ff">&lt;</span><span style="color: #800000">AlternativeType </span><span style="color: #ff0000">Name</span><span style="color: #0000ff">="vl::collections::SortedList&amp;lt;*,*&amp;gt;"</span><span style="color: #0000ff">/&gt;</span>
    <span style="color: #0000ff">&lt;</span><span style="color: #800000">AlternativeType </span><span style="color: #ff0000">Name</span><span style="color: #0000ff">="vl::collections::Array&amp;lt;*,*&amp;gt;"</span><span style="color: #0000ff">/&gt;</span>
    <span style="color: #0000ff">&lt;</span><span style="color: #800000">DisplayString</span><span style="color: #0000ff">&gt;</span>{{ size={count} }}<span style="color: #0000ff">&lt;/</span><span style="color: #800000">DisplayString</span><span style="color: #0000ff">&gt;</span>
    <span style="color: #0000ff">&lt;</span><span style="color: #800000">Expand</span><span style="color: #0000ff">&gt;</span>
      <span style="color: #0000ff">&lt;</span><span style="color: #800000">Item </span><span style="color: #ff0000">Name</span><span style="color: #0000ff">="[size]"</span><span style="color: #0000ff">&gt;</span>count<span style="color: #0000ff">&lt;/</span><span style="color: #800000">Item</span><span style="color: #0000ff">&gt;</span>
      <span style="color: #0000ff">&lt;</span><span style="color: #800000">ArrayItems</span><span style="color: #0000ff">&gt;</span>
        <span style="color: #0000ff">&lt;</span><span style="color: #800000">Size</span><span style="color: #0000ff">&gt;</span>count<span style="color: #0000ff">&lt;/</span><span style="color: #800000">Size</span><span style="color: #0000ff">&gt;</span>
        <span style="color: #0000ff">&lt;</span><span style="color: #800000">ValuePointer</span><span style="color: #0000ff">&gt;</span>buffer<span style="color: #0000ff">&lt;/</span><span style="color: #800000">ValuePointer</span><span style="color: #0000ff">&gt;</span>
      <span style="color: #0000ff">&lt;/</span><span style="color: #800000">ArrayItems</span><span style="color: #0000ff">&gt;</span>
    <span style="color: #0000ff">&lt;/</span><span style="color: #800000">Expand</span><span style="color: #0000ff">&gt;</span>
  <span style="color: #0000ff">&lt;/</span><span style="color: #800000">Type</span><span style="color: #0000ff">&gt;</span>

  <span style="color: #0000ff">&lt;</span><span style="color: #800000">Type </span><span style="color: #ff0000">Name</span><span style="color: #0000ff">="vl::collections::Dictionary&amp;lt;*,*,*,*&amp;gt;"</span><span style="color: #0000ff">&gt;</span>
    <span style="color: #0000ff">&lt;</span><span style="color: #800000">AlternativeType </span><span style="color: #ff0000">Name</span><span style="color: #0000ff">="vl::collections::Group&amp;lt;*,*,*,*&amp;gt;"</span><span style="color: #0000ff">/&gt;</span>
    <span style="color: #0000ff">&lt;</span><span style="color: #800000">DisplayString</span><span style="color: #0000ff">&gt;</span>{{ size={keys.count} }}<span style="color: #0000ff">&lt;/</span><span style="color: #800000">DisplayString</span><span style="color: #0000ff">&gt;</span>
    <span style="color: #0000ff">&lt;</span><span style="color: #800000">Expand</span><span style="color: #0000ff">&gt;</span>
      <span style="color: #0000ff">&lt;</span><span style="color: #800000">Item </span><span style="color: #ff0000">Name</span><span style="color: #0000ff">="[size]"</span><span style="color: #0000ff">&gt;</span>keys.count<span style="color: #0000ff">&lt;/</span><span style="color: #800000">Item</span><span style="color: #0000ff">&gt;</span>
      <span style="color: #0000ff">&lt;</span><span style="color: #800000">Item </span><span style="color: #ff0000">Name</span><span style="color: #0000ff">="Keys"</span><span style="color: #0000ff">&gt;</span>keys<span style="color: #0000ff">&lt;/</span><span style="color: #800000">Item</span><span style="color: #0000ff">&gt;</span>
      <span style="color: #0000ff">&lt;</span><span style="color: #800000">Item </span><span style="color: #ff0000">Name</span><span style="color: #0000ff">="Values"</span><span style="color: #0000ff">&gt;</span>values<span style="color: #0000ff">&lt;/</span><span style="color: #800000">Item</span><span style="color: #0000ff">&gt;</span>
    <span style="color: #0000ff">&lt;/</span><span style="color: #800000">Expand</span><span style="color: #0000ff">&gt;</span>
  <span style="color: #0000ff">&lt;/</span><span style="color: #800000">Type</span><span style="color: #0000ff">&gt;</span>

  <span style="color: #0000ff">&lt;</span><span style="color: #800000">Type </span><span style="color: #ff0000">Name</span><span style="color: #0000ff">="vl::Ptr&amp;lt;*&amp;gt;"</span><span style="color: #0000ff">&gt;</span>
    <span style="color: #0000ff">&lt;</span><span style="color: #800000">AlternativeType </span><span style="color: #ff0000">Name</span><span style="color: #0000ff">="vl::ComPtr&amp;lt;*&amp;gt;"</span><span style="color: #0000ff">/&gt;</span>
    <span style="color: #0000ff">&lt;</span><span style="color: #800000">DisplayString </span><span style="color: #ff0000">Condition</span><span style="color: #0000ff">="reference == 0"</span><span style="color: #0000ff">&gt;</span>[empty]<span style="color: #0000ff">&lt;/</span><span style="color: #800000">DisplayString</span><span style="color: #0000ff">&gt;</span>
    <span style="color: #0000ff">&lt;</span><span style="color: #800000">DisplayString </span><span style="color: #ff0000">Condition</span><span style="color: #0000ff">="reference != 0"</span><span style="color: #0000ff">&gt;</span>{*reference}<span style="color: #0000ff">&lt;/</span><span style="color: #800000">DisplayString</span><span style="color: #0000ff">&gt;</span>
    <span style="color: #0000ff">&lt;</span><span style="color: #800000">Expand</span><span style="color: #0000ff">&gt;</span>
      <span style="color: #0000ff">&lt;</span><span style="color: #800000">Item </span><span style="color: #ff0000">Condition</span><span style="color: #0000ff">="reference != 0"</span><span style="color: #ff0000"> Name</span><span style="color: #0000ff">="[ptr]"</span><span style="color: #0000ff">&gt;</span>reference<span style="color: #0000ff">&lt;/</span><span style="color: #800000">Item</span><span style="color: #0000ff">&gt;</span>
    <span style="color: #0000ff">&lt;/</span><span style="color: #800000">Expand</span><span style="color: #0000ff">&gt;</span>
  <span style="color: #0000ff">&lt;/</span><span style="color: #800000">Type</span><span style="color: #0000ff">&gt;</span>

  <span style="color: #0000ff">&lt;</span><span style="color: #800000">Type </span><span style="color: #ff0000">Name</span><span style="color: #0000ff">="vl::Lazy&amp;lt;*&amp;gt;"</span><span style="color: #0000ff">&gt;</span>
    <span style="color: #0000ff">&lt;</span><span style="color: #800000">DisplayString </span><span style="color: #ff0000">Condition</span><span style="color: #0000ff">="internalValue.reference == 0"</span><span style="color: #0000ff">&gt;</span>[empty]<span style="color: #0000ff">&lt;/</span><span style="color: #800000">DisplayString</span><span style="color: #0000ff">&gt;</span>
    <span style="color: #0000ff">&lt;</span><span style="color: #800000">DisplayString </span><span style="color: #ff0000">Condition</span><span style="color: #0000ff">="internalValue.reference != 0 &amp;amp;&amp;amp; internalValue.reference-&gt;evaluated == false"</span><span style="color: #0000ff">&gt;</span>[not evaluated]<span style="color: #0000ff">&lt;/</span><span style="color: #800000">DisplayString</span><span style="color: #0000ff">&gt;</span>
    <span style="color: #0000ff">&lt;</span><span style="color: #800000">DisplayString </span><span style="color: #ff0000">Condition</span><span style="color: #0000ff">="internalValue.reference != 0 &amp;amp;&amp;amp; internalValue.reference-&gt;evaluated == true"</span><span style="color: #0000ff">&gt;</span>{internalValue.reference-&gt;value}<span style="color: #0000ff">&lt;/</span><span style="color: #800000">DisplayString</span><span style="color: #0000ff">&gt;</span>
    <span style="color: #0000ff">&lt;</span><span style="color: #800000">Expand</span><span style="color: #0000ff">&gt;</span>
      <span style="color: #0000ff">&lt;</span><span style="color: #800000">Item </span><span style="color: #ff0000">Condition</span><span style="color: #0000ff">="internalValue.reference != 0 &amp;amp;&amp;amp; internalValue.reference-&gt;evaluated == true"</span><span style="color: #ff0000"> Name</span><span style="color: #0000ff">="[value]"</span><span style="color: #0000ff">&gt;</span>internalValue.reference-&gt;value<span style="color: #0000ff">&lt;/</span><span style="color: #800000">Item</span><span style="color: #0000ff">&gt;</span>
    <span style="color: #0000ff">&lt;/</span><span style="color: #800000">Expand</span><span style="color: #0000ff">&gt;</span>
  <span style="color: #0000ff">&lt;/</span><span style="color: #800000">Type</span><span style="color: #0000ff">&gt;</span>

  <span style="color: #0000ff">&lt;</span><span style="color: #800000">Type </span><span style="color: #ff0000">Name</span><span style="color: #0000ff">="vl::ObjectBox&amp;lt;*&amp;gt;"</span><span style="color: #0000ff">&gt;</span>
    <span style="color: #0000ff">&lt;</span><span style="color: #800000">DisplayString</span><span style="color: #0000ff">&gt;</span>{object}<span style="color: #0000ff">&lt;/</span><span style="color: #800000">DisplayString</span><span style="color: #0000ff">&gt;</span>
    <span style="color: #0000ff">&lt;</span><span style="color: #800000">Expand</span><span style="color: #0000ff">&gt;</span>
      <span style="color: #0000ff">&lt;</span><span style="color: #800000">ExpandedItem</span><span style="color: #0000ff">&gt;</span>object<span style="color: #0000ff">&lt;/</span><span style="color: #800000">ExpandedItem</span><span style="color: #0000ff">&gt;</span>
    <span style="color: #0000ff">&lt;/</span><span style="color: #800000">Expand</span><span style="color: #0000ff">&gt;</span>
  <span style="color: #0000ff">&lt;/</span><span style="color: #800000">Type</span><span style="color: #0000ff">&gt;</span>

  <span style="color: #0000ff">&lt;</span><span style="color: #800000">Type </span><span style="color: #ff0000">Name</span><span style="color: #0000ff">="vl::Nullable&amp;lt;*&amp;gt;"</span><span style="color: #0000ff">&gt;</span>
    <span style="color: #0000ff">&lt;</span><span style="color: #800000">DisplayString </span><span style="color: #ff0000">Condition</span><span style="color: #0000ff">="object == 0"</span><span style="color: #0000ff">&gt;</span>[empty]<span style="color: #0000ff">&lt;/</span><span style="color: #800000">DisplayString</span><span style="color: #0000ff">&gt;</span>
    <span style="color: #0000ff">&lt;</span><span style="color: #800000">DisplayString </span><span style="color: #ff0000">Condition</span><span style="color: #0000ff">="object != 0"</span><span style="color: #0000ff">&gt;</span>{*object}<span style="color: #0000ff">&lt;/</span><span style="color: #800000">DisplayString</span><span style="color: #0000ff">&gt;</span>
    <span style="color: #0000ff">&lt;</span><span style="color: #800000">Expand</span><span style="color: #0000ff">&gt;</span>
      <span style="color: #0000ff">&lt;</span><span style="color: #800000">ExpandedItem </span><span style="color: #ff0000">Condition</span><span style="color: #0000ff">="object != 0"</span><span style="color: #0000ff">&gt;</span>*object<span style="color: #0000ff">&lt;/</span><span style="color: #800000">ExpandedItem</span><span style="color: #0000ff">&gt;</span>
    <span style="color: #0000ff">&lt;/</span><span style="color: #800000">Expand</span><span style="color: #0000ff">&gt;</span>
  <span style="color: #0000ff">&lt;/</span><span style="color: #800000">Type</span><span style="color: #0000ff">&gt;</span>

<span style="color: #0000ff">&lt;/</span><span style="color: #800000">AutoVisualizer</span><span style="color: #0000ff">&gt;</span></pre></div><img src ="http://www.cppblog.com/vczh/aggbug/198665.html" width = "1" height = "1" /><br><br><div align=right><a style="text-decoration:none;" href="http://www.cppblog.com/vczh/" target="_blank">陈梓瀚(vczh)</a> 2013-03-21 11:55 <a href="http://www.cppblog.com/vczh/archive/2013/03/21/198665.html#Feedback" target="_blank" style="text-decoration:none;">发表评论</a></div>]]></description></item><item><title>使用VisualStudio完成自动化C++代码生成和编译工作（GacUI）</title><link>http://www.cppblog.com/vczh/archive/2012/01/14/164167.html</link><dc:creator>陈梓瀚(vczh)</dc:creator><author>陈梓瀚(vczh)</author><pubDate>Sat, 14 Jan 2012 06:09:00 GMT</pubDate><guid>http://www.cppblog.com/vczh/archive/2012/01/14/164167.html</guid><wfw:comment>http://www.cppblog.com/vczh/comments/164167.html</wfw:comment><comments>http://www.cppblog.com/vczh/archive/2012/01/14/164167.html#Feedback</comments><slash:comments>7</slash:comments><wfw:commentRss>http://www.cppblog.com/vczh/comments/commentRss/164167.html</wfw:commentRss><trackback:ping>http://www.cppblog.com/vczh/services/trackbacks/164167.html</trackback:ping><description><![CDATA[<div>&nbsp;&nbsp;&nbsp; GacUI终于进入制作dll的阶段了。昨天上传了一个新的工程，在<a style="text-decoration: underline" href="http://vlpp.codeplex.com" target="_blank">Vczh Library++3.0</a>（E:\Codeplex\vlpp\Workspace\Tools\Release\SideProjects\GacUI\GacUI.sln）。这里面一共有三个工程，有两个是工具，一个是dll。<br /><br />&nbsp;&nbsp;&nbsp; 为了编译出带反射的控件库，因此每一个控件都可以获得一个ITypeDescriptor对象。但是控件库一共有几十个类上千个函数，我不可能一个一个去实现的（请想想实现IDispatcher的时候）。根据<a style="text-decoration: underline" href="http://www.cppblog.com/vczh/archive/2012/01/11/164003.html" target="_blank">上一篇博客</a>讨论过技术，我将使用一个程序来读pdb生成C++代码。详细的计划如下：<br /><br />&nbsp;&nbsp;&nbsp; 1：制作一个_GacPDB工程。这是一个exe，但是是没用的，唯一的用处就是他引用了GacUI.dll所需要的所有源代码，然后靠编译器产生PDB文件。<br />&nbsp;&nbsp;&nbsp; 2：制作一个_TranslatePDBtoXML工程。这是一个exe，从PDB抽取类声明。<br />&nbsp;&nbsp;&nbsp; 3：制作一个_TranslateXMltoCode。顾名思义，不过现在还没做，原理是一样的。<br />&nbsp;&nbsp;&nbsp; 4：GacUI.dll。这个dll包含了所有的控件的实现，还有_TranslateXMLtoCode产生的所有代码。<br /><br />&nbsp;&nbsp;&nbsp; 现在我的目标是，先编译_Translate*工程，然后编译_GacPDB产生pdb后自动调用它们，生成代码结束之后开始合并编译GacUI.dll。所有的这些东西都需要在VisualStudio的&#8220;Rebuild Solution&#8221;里面完成。为了完成这个目标，我创建这些工程之后，按照下面的方法修改了工程属性：
<div style="border-bottom: #cccccc 1px solid; border-left: #cccccc 1px solid; padding-bottom: 4px; background-color: #eeeeee; padding-left: 4px; width: 98%; padding-right: 5px; font-size: 13px; word-break: break-all; border-top: #cccccc 1px solid; border-right: #cccccc 1px solid; padding-top: 4px"><!--<br /><br />Code highlighting produced by Actipro CodeHighlighter (freeware)<br />http://www.CodeHighlighter.com/<br /><br />--><span style="color: #008080">&nbsp;1</span>&nbsp;<span style="color: #000000">_TranslatePDBtoXML:<br /></span><span style="color: #008080">&nbsp;2</span>&nbsp;<span style="color: #000000">&nbsp;&nbsp;&nbsp;&nbsp;post&nbsp;build&nbsp;action:<br /></span><span style="color: #008080">&nbsp;3</span>&nbsp;<span style="color: #000000">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;copy&nbsp;$(ProjectDir)msdia100.dll&nbsp;$(SolutionDir)$(Configuration)\msdia100.dll<br /></span><span style="color: #008080">&nbsp;4</span>&nbsp;<span style="color: #000000">_GenPDB:<br /></span><span style="color: #008080">&nbsp;5</span>&nbsp;<span style="color: #000000">&nbsp;&nbsp;&nbsp;&nbsp;references:<br /></span><span style="color: #008080">&nbsp;6</span>&nbsp;<span style="color: #000000">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;_TranslatePDBtoXML<br /></span><span style="color: #008080">&nbsp;7</span>&nbsp;<span style="color: #000000">&nbsp;&nbsp;&nbsp;&nbsp;post&nbsp;build&nbsp;action:<br /></span><span style="color: #008080">&nbsp;8</span>&nbsp;<span style="color: #000000">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;$(SolutionDir)$(Configuration)\_TranslatePDBtoXML.exe&nbsp;$(SolutionDir)Debug\_GenPDB.pdb&nbsp;$(SolutionDir)_GenPDB.xml<br /></span><span style="color: #008080">&nbsp;9</span>&nbsp;<span style="color: #000000">GacUI:<br /></span><span style="color: #008080">10</span>&nbsp;<span style="color: #000000">&nbsp;&nbsp;&nbsp;&nbsp;references:<br /></span><span style="color: #008080">11</span>&nbsp;<span style="color: #000000">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;_GenPDB</span></div><br />&nbsp;&nbsp;&nbsp; 1：工程A引用了工程B的话，那么只有当B完全编译好之后才会编译A。因此上面的配置将阻止三个工程平行编译，强制他们按照_TranslatePDBtoXML、_GenPDB和GacUI的顺序来。<br />&nbsp;&nbsp;&nbsp; 2：_TranslatePDBtoXML编译好之后，会把它依赖的msdia100.dll复制到编译出来的exe旁边，以供接下来调用。<br />&nbsp;&nbsp;&nbsp; 3：_GenPDB编译好之后，pdb已经产生了。这个时候它会自动调用上一步编译出来的_TranslatePDBtoXML，读取pdb，输出xml<br />&nbsp;&nbsp;&nbsp; 4：（接下来要做的）调用_TranslateXMLtoCode，输入xml，输出C++代码<br />&nbsp;&nbsp;&nbsp; 5：这个时候，生成的C++代码已经就绪了，所以开始编译GacUI。<br /><br />&nbsp;&nbsp;&nbsp; 附加的好处还有一个。因为_GenPDB引用了GacUI的cpp，所以当GacUI的源代码修改的时候，_GenPDB也会感应到，从而在下次编译GacUI的时候先开始编译_GenPDB。并且因为GacUI依赖了_GenPDB，所以_GenPDB仍然会先编译。而且这种依赖关系是无害的，因为_GenPDB没有输出lib，因此GacUI.dll在运行的时候完全不需要_GenPDB.exe的存在。<br /><br />&nbsp;&nbsp;&nbsp; 好了。那把一个个的cpp文件添加到_GenPDB也是在太麻烦了，所以我投机取巧了一下：
<div style="border-bottom: #cccccc 1px solid; border-left: #cccccc 1px solid; padding-bottom: 4px; background-color: #eeeeee; padding-left: 4px; width: 98%; padding-right: 5px; font-size: 13px; word-break: break-all; border-top: #cccccc 1px solid; border-right: #cccccc 1px solid; padding-top: 4px"><!--<br /><br />Code highlighting produced by Actipro CodeHighlighter (freeware)<br />http://www.CodeHighlighter.com/<br /><br />--><span style="color: #008080">&nbsp;1</span>&nbsp;<span style="color: #000000">#include&nbsp;</span><span style="color: #000000">"</span><span style="color: #000000">..\..\..\..\..\Candidate\GUI\GUI\Controls\GuiApplication.cpp</span><span style="color: #000000">"</span><span style="color: #000000"><br /></span><span style="color: #008080">&nbsp;2</span>&nbsp;<span style="color: #000000">#include&nbsp;</span><span style="color: #000000">"</span><span style="color: #000000">..\..\..\..\..\Candidate\GUI\GUI\Controls\GuiBasicControls.cpp</span><span style="color: #000000">"</span><span style="color: #000000"><br /></span><span style="color: #008080">&nbsp;3</span>&nbsp;<span style="color: #000000">#include&nbsp;</span><span style="color: #000000">"</span><span style="color: #000000">..\..\..\..\..\Candidate\GUI\GUI\Controls\GuiListControls.cpp</span><span style="color: #000000">"</span><span style="color: #000000"><br /></span><span style="color: #008080">&nbsp;4</span>&nbsp;<span style="color: #000000">#include&nbsp;</span><span style="color: #000000">"</span><span style="color: #000000">..\..\..\..\..\Candidate\GUI\GUI\Controls\GuiTextControls.cpp</span><span style="color: #000000">"</span><span style="color: #000000"><br /></span><span style="color: #008080">&nbsp;5</span>&nbsp;<span style="color: #000000">#include&nbsp;</span><span style="color: #000000">"</span><span style="color: #000000">..\..\..\..\..\Candidate\GUI\GUI\Controls\GuiWindowControls.cpp</span><span style="color: #000000">"</span><span style="color: #000000"><br /></span><span style="color: #008080">&nbsp;6</span>&nbsp;<span style="color: #000000"></span><span style="color: #008000">//</span><span style="color: #008000">---------------------------------------------------------------</span><span style="color: #008000"><br /></span><span style="color: #008080">&nbsp;7</span>&nbsp;<span style="color: #008000"></span><span style="color: #000000">#include&nbsp;</span><span style="color: #000000">"</span><span style="color: #000000">..\..\..\..\..\Candidate\GUI\GUI\Controls\ExtendedControls\GuiComboControls.cpp</span><span style="color: #000000">"</span><span style="color: #000000"><br /></span><span style="color: #008080">&nbsp;8</span>&nbsp;<span style="color: #000000">#include&nbsp;</span><span style="color: #000000">"</span><span style="color: #000000">..\..\..\..\..\Candidate\GUI\GUI\Controls\ExtendedControls\GuiContainerControls.cpp</span><span style="color: #000000">"</span><span style="color: #000000"><br /></span><span style="color: #008080">&nbsp;9</span>&nbsp;<span style="color: #000000">#include&nbsp;</span><span style="color: #000000">"</span><span style="color: #000000">..\..\..\..\..\Candidate\GUI\GUI\Controls\ExtendedControls\GuiListViewControls.cpp</span><span style="color: #000000">"</span><span style="color: #000000"><br /></span><span style="color: #008080">10</span>&nbsp;<span style="color: #000000">#include&nbsp;</span><span style="color: #000000">"</span><span style="color: #000000">..\..\..\..\..\Candidate\GUI\GUI\Controls\ExtendedControls\GuiMenuControls.cpp</span><span style="color: #000000">"</span><span style="color: #000000"><br /></span><span style="color: #008080">11</span>&nbsp;<span style="color: #000000">#include&nbsp;</span><span style="color: #000000">"</span><span style="color: #000000">..\..\..\..\..\Candidate\GUI\GUI\Controls\ExtendedControls\GuiTextListControls.cpp</span><span style="color: #000000">"</span><span style="color: #000000"><br /></span><span style="color: #008080">12</span>&nbsp;<span style="color: #000000">#include&nbsp;</span><span style="color: #000000">"</span><span style="color: #000000">..\..\..\..\..\Candidate\GUI\GUI\Controls\ExtendedControls\GuiTreeViewControls.cpp</span><span style="color: #000000">"</span><span style="color: #000000"><br /></span><span style="color: #008080">13</span>&nbsp;<span style="color: #000000"></span><span style="color: #008000">//</span><span style="color: #008000">---------------------------------------------------------------</span><span style="color: #008000"><br /></span><span style="color: #008080">14</span>&nbsp;<span style="color: #008000"></span><span style="color: #000000">#include&nbsp;</span><span style="color: #000000">"</span><span style="color: #000000">..\..\..\..\..\Candidate\GUI\GUI\Controls\Styles\GuiCommonStyles.cpp</span><span style="color: #000000">"</span><span style="color: #000000"><br /></span><span style="color: #008080">15</span>&nbsp;<span style="color: #000000">#include&nbsp;</span><span style="color: #000000">"</span><span style="color: #000000">..\..\..\..\..\Candidate\GUI\GUI\Controls\Styles\GuiWin7Styles.cpp</span><span style="color: #000000">"</span><span style="color: #000000"><br /></span><span style="color: #008080">16</span>&nbsp;<span style="color: #000000"></span><span style="color: #008000">//</span><span style="color: #008000">---------------------------------------------------------------</span><span style="color: #008000"><br /></span><span style="color: #008080">17</span>&nbsp;<span style="color: #008000"></span><span style="color: #000000">#include&nbsp;</span><span style="color: #000000">"</span><span style="color: #000000">..\..\..\..\..\Candidate\GUI\GUI\GraphicsElement\GuiGraphicsComposition.cpp</span><span style="color: #000000">"</span><span style="color: #000000"><br /></span><span style="color: #008080">18</span>&nbsp;<span style="color: #000000">#include&nbsp;</span><span style="color: #000000">"</span><span style="color: #000000">..\..\..\..\..\Candidate\GUI\GUI\GraphicsElement\GuiGraphicsElement.cpp</span><span style="color: #000000">"</span><span style="color: #000000"><br /></span><span style="color: #008080">19</span>&nbsp;<span style="color: #000000">#include&nbsp;</span><span style="color: #000000">"</span><span style="color: #000000">..\..\..\..\..\Candidate\GUI\GUI\GraphicsElement\GuiGraphicsEventReceiver.cpp</span><span style="color: #000000">"</span><span style="color: #000000"><br /></span><span style="color: #008080">20</span>&nbsp;<span style="color: #000000">#include&nbsp;</span><span style="color: #000000">"</span><span style="color: #000000">..\..\..\..\..\Candidate\GUI\GUI\GraphicsElement\GuiGraphicsHost.cpp</span><span style="color: #000000">"</span><span style="color: #000000"><br /></span><span style="color: #008080">21</span>&nbsp;<span style="color: #000000">#include&nbsp;</span><span style="color: #000000">"</span><span style="color: #000000">..\..\..\..\..\Candidate\GUI\GUI\GraphicsElement\GuiGraphicsTextElement.cpp</span><span style="color: #000000">"</span><span style="color: #000000"><br /></span><span style="color: #008080">22</span>&nbsp;<span style="color: #000000"></span><span style="color: #008000">//</span><span style="color: #008000">---------------------------------------------------------------</span><span style="color: #008000"><br /></span><span style="color: #008080">23</span>&nbsp;<span style="color: #008000"></span><span style="color: #000000">#include&nbsp;</span><span style="color: #000000">"</span><span style="color: #000000">..\..\..\..\..\Candidate\GUI\GUI\NativeWindow\GuiNativeWindow.cpp</span><span style="color: #000000">"</span><span style="color: #000000"><br /></span><span style="color: #008080">24</span>&nbsp;<span style="color: #000000">#include&nbsp;</span><span style="color: #000000">"</span><span style="color: #000000">..\..\..\..\..\Candidate\GUI\GUI\NativeWindow\Windows\WinNativeWindow.cpp</span><span style="color: #000000">"</span><span style="color: #000000"><br /></span><span style="color: #008080">25</span>&nbsp;<span style="color: #000000"></span><span style="color: #008000">//</span><span style="color: #008000">---------------------------------------------------------------</span><span style="color: #008000"><br /></span><span style="color: #008080">26</span>&nbsp;<span style="color: #008000"></span><span style="color: #000000">#include&nbsp;</span><span style="color: #000000">"</span><span style="color: #000000">..\..\..\..\..\Candidate\GUI\GUI\Reflection\GuiTypeDescriptor.cpp</span><span style="color: #000000">"</span><span style="color: #000000"><br /></span><span style="color: #008080">27</span>&nbsp;<span style="color: #000000"></span><span style="color: #008000">//</span><span style="color: #008000">---------------------------------------------------------------</span><span style="color: #008000"><br /></span><span style="color: #008080">28</span>&nbsp;<span style="color: #008000"></span><span style="color: #000000">#include&nbsp;</span><span style="color: #000000">"</span><span style="color: #000000">..\..\..\..\..\Library\Basic.cpp</span><span style="color: #000000">"</span><span style="color: #000000"><br /></span><span style="color: #008080">29</span>&nbsp;<span style="color: #000000">#include&nbsp;</span><span style="color: #000000">"</span><span style="color: #000000">..\..\..\..\..\Library\Exception.cpp</span><span style="color: #000000">"</span><span style="color: #000000"><br /></span><span style="color: #008080">30</span>&nbsp;<span style="color: #000000">#include&nbsp;</span><span style="color: #000000">"</span><span style="color: #000000">..\..\..\..\..\Library\String.cpp</span><span style="color: #000000">"</span><span style="color: #000000"><br /></span><span style="color: #008080">31</span>&nbsp;<span style="color: #000000">#include&nbsp;</span><span style="color: #000000">"</span><span style="color: #000000">..\..\..\..\..\Library\Threading.cpp</span><span style="color: #000000">"</span><span style="color: #000000"><br /></span><span style="color: #008080">32</span>&nbsp;<span style="color: #000000">#include&nbsp;</span><span style="color: #000000">"</span><span style="color: #000000">..\..\..\..\..\Library\Collections\Operation.cpp</span><span style="color: #000000">"</span><span style="color: #000000"><br /></span><span style="color: #008080">33</span>&nbsp;<span style="color: #000000"></span><span style="color: #008000">//</span><span style="color: #008000">---------------------------------------------------------------</span><span style="color: #008000"><br /></span><span style="color: #008080">34</span>&nbsp;<span style="color: #008000"></span><span style="color: #000000">#include&nbsp;</span><span style="color: #000000">&lt;</span><span style="color: #000000">Windows.h</span><span style="color: #000000">&gt;</span><span style="color: #000000"><br /></span><span style="color: #008080">35</span>&nbsp;<span style="color: #000000"><br /></span><span style="color: #008080">36</span>&nbsp;<span style="color: #000000"></span><span style="color: #0000ff">int</span><span style="color: #000000">&nbsp;CALLBACK&nbsp;WinMain(HINSTANCE&nbsp;hInstance,&nbsp;HINSTANCE&nbsp;hPrevInstance,&nbsp;LPSTR&nbsp;lpCmdLine,&nbsp;</span><span style="color: #0000ff">int</span><span style="color: #000000">&nbsp;CmdShow)<br /></span><span style="color: #008080">37</span>&nbsp;<span style="color: #000000">{<br /></span><span style="color: #008080">38</span>&nbsp;<span style="color: #000000">&nbsp;&nbsp;&nbsp;&nbsp;</span><span style="color: #0000ff">return</span><span style="color: #000000">&nbsp;</span><span style="color: #000000">0</span><span style="color: #000000">;<br /></span><span style="color: #008080">39</span>&nbsp;<span style="color: #000000">}</span></div></div><br />&nbsp;&nbsp;&nbsp; 啊哈哈哈哈（拖走<br /><br />&nbsp;&nbsp;&nbsp; VisualStudio的功能是强大的。只要善于使用，或者配合MSBuild，所起到的威力将毫不亚于某些著名工具链。而且VisualStudio编译器产生的文件，基本上VisualStudio都有提供API供你阅读，所以也可以做很多事情，譬如我这篇文章说的这样，充当了一个编译器的扩展，而且完美集成。<img src ="http://www.cppblog.com/vczh/aggbug/164167.html" width = "1" height = "1" /><br><br><div align=right><a style="text-decoration:none;" href="http://www.cppblog.com/vczh/" target="_blank">陈梓瀚(vczh)</a> 2012-01-14 14:09 <a href="http://www.cppblog.com/vczh/archive/2012/01/14/164167.html#Feedback" target="_blank" style="text-decoration:none;">发表评论</a></div>]]></description></item><item><title>C++实用技巧（四）</title><link>http://www.cppblog.com/vczh/archive/2010/06/27/118829.html</link><dc:creator>陈梓瀚(vczh)</dc:creator><author>陈梓瀚(vczh)</author><pubDate>Sun, 27 Jun 2010 12:19:00 GMT</pubDate><guid>http://www.cppblog.com/vczh/archive/2010/06/27/118829.html</guid><wfw:comment>http://www.cppblog.com/vczh/comments/118829.html</wfw:comment><comments>http://www.cppblog.com/vczh/archive/2010/06/27/118829.html#Feedback</comments><slash:comments>16</slash:comments><wfw:commentRss>http://www.cppblog.com/vczh/comments/commentRss/118829.html</wfw:commentRss><trackback:ping>http://www.cppblog.com/vczh/services/trackbacks/118829.html</trackback:ping><description><![CDATA[&nbsp;&nbsp;&nbsp; 复杂的东西写多了，如今写点简单的好了。由于功能上的需要，<a style="TEXT-DECORATION: underline" href="http://vlpp.codeplex.com/" target=_blank>Vczh Library++3.0</a>被我搞得很离谱。为了开发维护的遍历、减少粗心犯下的错误以及增强单元测试、回归测试和测试工具，因此记录下一些开发上的小技巧，以便抛砖引玉，造福他人。欢迎高手来喷，菜鸟膜拜。<br><br>&nbsp;&nbsp;&nbsp; <a style="TEXT-DECORATION: underline" href="http://www.cppblog.com/vczh/archive/2010/06/24/118635.html" target=_blank>之前的文章</a>讲了指针和内存的一些问题，今天说一下单元测试的问题。如果在团队里面没有对单元测试的框架有要求的话，其实我们可以使用一个最简单的方法来搭建在IDE里面运行的单元测试框架，整个框架只需十几行代码。我们先来考虑一下功能最少的单元测试框架需要完成什么样的内容。首先我们要运行一个一个的测试用例，其次在一个测试用例里面我们要检查一些条件是否成立。举个例子，我们写一个函数将两个字符串连接起来，一般来说要进行下面的测试：<br>
<div style="BORDER-BOTTOM: #cccccc 1px solid; BORDER-LEFT: #cccccc 1px solid; PADDING-BOTTOM: 4px; BACKGROUND-COLOR: #eeeeee; PADDING-LEFT: 4px; WIDTH: 98%; PADDING-RIGHT: 5px; FONT-SIZE: 13px; WORD-BREAK: break-all; BORDER-TOP: #cccccc 1px solid; BORDER-RIGHT: #cccccc 1px solid; PADDING-TOP: 4px"><span style="COLOR: #008080">&nbsp;1</span>&nbsp;<span style="COLOR: #000000">#include&nbsp;</span><span style="COLOR: #000000">"</span><span style="COLOR: #000000">MyUnitTestFramework.h</span><span style="COLOR: #000000">"</span><span style="COLOR: #008000">//</span><span style="COLOR: #008000">等一下我们会展示一下如何用最少的代码完成这个头文件的内容</span><span style="COLOR: #008000"><br></span><span style="COLOR: #008080">&nbsp;2</span>&nbsp;<span style="COLOR: #008000"></span><span style="COLOR: #000000">#include&nbsp;</span><span style="COLOR: #000000">"</span><span style="COLOR: #000000"><img src="http://www.cppblog.com/Images/dot.gif"></span><span style="COLOR: #000000">"</span><span style="COLOR: #000000"><br></span><span style="COLOR: #008080">&nbsp;3</span>&nbsp;<span style="COLOR: #000000"><br></span><span style="COLOR: #008080">&nbsp;4</span>&nbsp;<span style="COLOR: #000000">TEST_CASE(StringConcat)<br></span><span style="COLOR: #008080">&nbsp;5</span>&nbsp;<span style="COLOR: #000000">{<br></span><span style="COLOR: #008080">&nbsp;6</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;TEST_ASSERT(concat(</span><span style="COLOR: #000000">"</span><span style="COLOR: #000000">a</span><span style="COLOR: #000000">"</span><span style="COLOR: #000000">,&nbsp;</span><span style="COLOR: #000000">"</span><span style="COLOR: #000000">b</span><span style="COLOR: #000000">"</span><span style="COLOR: #000000">)</span><span style="COLOR: #000000">==</span><span style="COLOR: #000000">"</span><span style="COLOR: #000000">ab</span><span style="COLOR: #000000">"</span><span style="COLOR: #000000">);<br></span><span style="COLOR: #008080">&nbsp;7</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;TEST_ASSERT(concat(</span><span style="COLOR: #000000">"</span><span style="COLOR: #000000">a</span><span style="COLOR: #000000">"</span><span style="COLOR: #000000">,&nbsp;</span><span style="COLOR: #000000">""</span><span style="COLOR: #000000">)</span><span style="COLOR: #000000">==</span><span style="COLOR: #000000">"</span><span style="COLOR: #000000">a</span><span style="COLOR: #000000">"</span><span style="COLOR: #000000">);<br></span><span style="COLOR: #008080">&nbsp;8</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;TEST_ASSERT(concat(</span><span style="COLOR: #000000">""</span><span style="COLOR: #000000">,&nbsp;</span><span style="COLOR: #000000">"</span><span style="COLOR: #000000">b</span><span style="COLOR: #000000">"</span><span style="COLOR: #000000">)</span><span style="COLOR: #000000">==</span><span style="COLOR: #000000">"</span><span style="COLOR: #000000">b</span><span style="COLOR: #000000">"</span><span style="COLOR: #000000">);<br></span><span style="COLOR: #008080">&nbsp;9</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;TEST_ASSERT(concat(</span><span style="COLOR: #000000">""</span><span style="COLOR: #000000">,&nbsp;</span><span style="COLOR: #000000">""</span><span style="COLOR: #000000">)</span><span style="COLOR: #000000">==</span><span style="COLOR: #000000">""</span><span style="COLOR: #000000">);<br></span><span style="COLOR: #008080">10</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;<img src="http://www.cppblog.com/Images/dot.gif">.<br></span><span style="COLOR: #008080">11</span>&nbsp;<span style="COLOR: #000000">}<br></span><span style="COLOR: #008080">12</span>&nbsp;<span style="COLOR: #000000"><br></span><span style="COLOR: #008080">13</span>&nbsp;<span style="COLOR: #000000"></span><span style="COLOR: #0000ff">int</span><span style="COLOR: #000000">&nbsp;wmain()<br></span><span style="COLOR: #008080">14</span>&nbsp;<span style="COLOR: #000000">{<br></span><span style="COLOR: #008080">15</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;</span><span style="COLOR: #0000ff">return</span><span style="COLOR: #000000">&nbsp;</span><span style="COLOR: #000000">0</span><span style="COLOR: #000000">;<br></span><span style="COLOR: #008080">16</span>&nbsp;<span style="COLOR: #000000">}</span></div>
<br>&nbsp;&nbsp;&nbsp; 如果我们的单元测试框架可以这么写，那显然做起什么事情来都会方便很多，而且不需要向一些其他的测试框架一样注册一大堆东西，或者是写一大堆配置函数。当然这次我们只做功能最少的测试框架，这个框架除了运行测试以外，不会有其他功能，譬如选择哪些测试可以运行啦，还是在出错的时候log一些什么啦之类。之所以要在IDE里面运行，是因为我们如果做到TEST_ASSERT中出现false的话，立刻在该行崩溃，那么IDE就会帮你定位到出错的TEST_ASSERT中去，然后给你显示所有的上下文信息，譬如说callstack啦什么的。友好的工具不用简直对不起自己啊，干吗非得把单元测试做得那么复杂捏，凡是单元测试，总是要全部运行通过才能提交代码的。<br><br>&nbsp;&nbsp;&nbsp; 那么我们来看看上面的单元测试的代码。首先写了TEST_CASE的那个地方，大括号里面的代码会自动运行。其次TEST_ASSERT会在表达式是false的时候崩溃。先从简单的入手吧。如何制造崩溃呢？最简单的办法就是抛异常：<br>
<div style="BORDER-BOTTOM: #cccccc 1px solid; BORDER-LEFT: #cccccc 1px solid; PADDING-BOTTOM: 4px; BACKGROUND-COLOR: #eeeeee; PADDING-LEFT: 4px; WIDTH: 98%; PADDING-RIGHT: 5px; FONT-SIZE: 13px; WORD-BREAK: break-all; BORDER-TOP: #cccccc 1px solid; BORDER-RIGHT: #cccccc 1px solid; PADDING-TOP: 4px"><span style="COLOR: #008080">1</span>&nbsp;<span style="COLOR: #0000ff">#define</span><span style="COLOR: #000000">&nbsp;TEST_ASSERT(e)&nbsp;do(if(!(e))throw&nbsp;"今晚没饭吃。";}while(0)</span></div>
<br>&nbsp;&nbsp;&nbsp; 这里面有两个要注意的地方。首先e要加上小括号，不然取反操作符就有可能做出错误的行为。譬如说当e是a+b==c的时候，加了小括号就变成if(!(a+b==c))...，没有加小括号就变成if(!a+b==c)...，意思就完全变了。第二个主意的地方是我使用do{...}while(0)把语句包围起来了。这样做的好处是可以在任何时候TEST_ASSERT(e)都像一个语句。譬如我们可能这么写：<br>
<div style="BORDER-BOTTOM: #cccccc 1px solid; BORDER-LEFT: #cccccc 1px solid; PADDING-BOTTOM: 4px; BACKGROUND-COLOR: #eeeeee; PADDING-LEFT: 4px; WIDTH: 98%; PADDING-RIGHT: 5px; FONT-SIZE: 13px; WORD-BREAK: break-all; BORDER-TOP: #cccccc 1px solid; BORDER-RIGHT: #cccccc 1px solid; PADDING-TOP: 4px"><span style="COLOR: #008080">1</span>&nbsp;<span style="COLOR: #0000ff">if</span><span style="COLOR: #000000">(a)<br></span><span style="COLOR: #008080">2</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;TEST_ASSERT(x1);<br></span><span style="COLOR: #008080">3</span>&nbsp;<span style="COLOR: #000000"></span><span style="COLOR: #0000ff">else</span><span style="COLOR: #000000">&nbsp;</span><span style="COLOR: #0000ff">if</span><span style="COLOR: #000000">(b)<br></span><span style="COLOR: #008080">4</span>&nbsp;<span style="COLOR: #000000">{<br></span><span style="COLOR: #008080">5</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;TEST_ASSERT(x2);<br></span><span style="COLOR: #008080">6</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;TEST_ASSERT(x3);<br></span><span style="COLOR: #008080">7</span>&nbsp;<span style="COLOR: #000000">}</span></div>
<br>&nbsp;&nbsp;&nbsp; 如果没有do{...}while(0)包围起来，这个else就会被绑定到宏里面的那个if，你的代码就被偷偷改掉了。<br><br>&nbsp;&nbsp;&nbsp; 那么现在剩下TEST_CASE(x){y}了。什么东西可以在main函数外面自动运行呢？这个我想熟悉C++的人都会知道，就是全局变量的构造函数啦。所以TEST_CASE(x){y}那个大括号里面的y只能在全局变量的构造函数里面调用。但是我们知道写一个类的时候，构造函数的大括号写完了，后面还有类的大括号，全局变量的名称，和最终的一个分号。为了把这些去掉，那么显然{y}应该属于一个普通的函数。那么全局变量如何能够使用这个函数呢？方法很简单，把函数前置声明一下就行了：<br>
<div style="BORDER-BOTTOM: #cccccc 1px solid; BORDER-LEFT: #cccccc 1px solid; PADDING-BOTTOM: 4px; BACKGROUND-COLOR: #eeeeee; PADDING-LEFT: 4px; WIDTH: 98%; PADDING-RIGHT: 5px; FONT-SIZE: 13px; WORD-BREAK: break-all; BORDER-TOP: #cccccc 1px solid; BORDER-RIGHT: #cccccc 1px solid; PADDING-TOP: 4px"><span style="COLOR: #008080">&nbsp;1</span>&nbsp;<span style="COLOR: #0000ff">#define</span><span style="COLOR: #000000">&nbsp;TEST_CASE(NAME)&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;\</span><span style="COLOR: #000000"><br></span><span style="COLOR: #008080">&nbsp;2</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span style="COLOR: #0000ff">extern</span><span style="COLOR: #000000">&nbsp;</span><span style="COLOR: #0000ff">void</span><span style="COLOR: #000000">&nbsp;TESTCASE_##NAME();&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;\<br></span><span style="COLOR: #008080">&nbsp;3</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span style="COLOR: #0000ff">namespace</span><span style="COLOR: #000000">&nbsp;vl_unittest_executors&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;\<br></span><span style="COLOR: #008080">&nbsp;4</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;{&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;\<br></span><span style="COLOR: #008080">&nbsp;5</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span style="COLOR: #0000ff">class</span><span style="COLOR: #000000">&nbsp;TESTCASE_RUNNER_##NAME&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;\<br></span><span style="COLOR: #008080">&nbsp;6</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;{&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;\<br></span><span style="COLOR: #008080">&nbsp;7</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span style="COLOR: #0000ff">public</span><span style="COLOR: #000000">:&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;\<br></span><span style="COLOR: #008080">&nbsp;8</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;TESTCASE_RUNNER_##NAME()&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;\<br></span><span style="COLOR: #008080">&nbsp;9</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;{&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;\<br></span><span style="COLOR: #008080">10</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;TESTCASE_##NAME();&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;\<br></span><span style="COLOR: #008080">11</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;\<br></span><span style="COLOR: #008080">12</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}&nbsp;TESTCASE_RUNNER_##NAME##_INSTANCE;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;\<br></span><span style="COLOR: #008080">13</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;\<br></span><span style="COLOR: #008080">14</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span style="COLOR: #0000ff">void</span><span style="COLOR: #000000">&nbsp;TESTCASE_##NAME()</span></div>
<br>&nbsp;&nbsp;&nbsp; 那我们来看看TEST_CASE(x){y}究竟会被翻译成什么代码：<br>
<div style="BORDER-BOTTOM: #cccccc 1px solid; BORDER-LEFT: #cccccc 1px solid; PADDING-BOTTOM: 4px; BACKGROUND-COLOR: #eeeeee; PADDING-LEFT: 4px; WIDTH: 98%; PADDING-RIGHT: 5px; FONT-SIZE: 13px; WORD-BREAK: break-all; BORDER-TOP: #cccccc 1px solid; BORDER-RIGHT: #cccccc 1px solid; PADDING-TOP: 4px"><span style="COLOR: #008080">&nbsp;1</span>&nbsp;<span style="COLOR: #0000ff">extern</span><span style="COLOR: #000000">&nbsp;</span><span style="COLOR: #0000ff">void</span><span style="COLOR: #000000">&nbsp;TESTCASE_x();<br></span><span style="COLOR: #008080">&nbsp;2</span>&nbsp;<span style="COLOR: #000000"></span><span style="COLOR: #0000ff">namespace</span><span style="COLOR: #000000">&nbsp;vl_unittest_executors<br></span><span style="COLOR: #008080">&nbsp;3</span>&nbsp;<span style="COLOR: #000000">{<br></span><span style="COLOR: #008080">&nbsp;4</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;</span><span style="COLOR: #0000ff">class</span><span style="COLOR: #000000">&nbsp;TESTCASE_RUNNER_x<br></span><span style="COLOR: #008080">&nbsp;5</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;{<br></span><span style="COLOR: #008080">&nbsp;6</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;</span><span style="COLOR: #0000ff">public</span><span style="COLOR: #000000">:<br></span><span style="COLOR: #008080">&nbsp;7</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;TESTCASE_RUNNER_x()<br></span><span style="COLOR: #008080">&nbsp;8</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;{<br></span><span style="COLOR: #008080">&nbsp;9</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;TESTCASE_x();<br></span><span style="COLOR: #008080">10</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}<br></span><span style="COLOR: #008080">11</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;}&nbsp;TESTCASE_RUNNER_x_INSTANCE;<br></span><span style="COLOR: #008080">12</span>&nbsp;<span style="COLOR: #000000">}<br></span><span style="COLOR: #008080">13</span>&nbsp;<span style="COLOR: #000000"></span><span style="COLOR: #0000ff">void</span><span style="COLOR: #000000">&nbsp;TESTCASE_x(){y}</span></div>
<br>&nbsp;&nbsp;&nbsp; 到了这里是不是很清楚了捏，首先在main函数运行之前TESTCASE_RUNNER_x_INSTANCE变量会初始化，然后调用TESTCASE_RUNNER_x的构造函数，最后运行函数TESTCASE_x，该函数的内容显然就是{y}了。这里还能学到宏是如何连接两个名字成为一个名字，和如何写多行的宏的。<br><br>&nbsp;&nbsp;&nbsp; 于是MyUnittestFramework.h就包含这两个宏，其他啥都没有，是不是很方便呢？打开Visual C++，建立一个工程，引用这个头文件，然后写你的单元测试，最后F5就运行了，多方便啊，啊哈哈哈。<br><br>&nbsp;&nbsp;&nbsp; 这里需要注意一点，那些单元测试的顺序是不受到保证的，特别是你使用了多个cpp文件的情况下。于是你在使用这个测试框架的同时，会被迫保证执行一次单元测试不会对你的全局状态带来什么副作用，以便两个测试用例交换顺序执行的时候仍然能稳定地产生相同的结果。这对你写单元测试有帮助，而且为了让你的代码能够被这么测试，你的代码也会写的有条理，不会依赖全局状态，真是一举两得也。而且说不定单元测试用例比你的全局变量的初始化还先执行呢，因此为了使用这个测试框架，你将会不得不把你的全局变量隐藏在一个cpp里面，而暴露出随时可以被调用的一组函数出来。这样也可以让你的代码在使用全局状态的时候更加安全。<br><br>&nbsp;&nbsp;&nbsp; 今天就讲到这里了。下一篇要写什么我还没想好，到时候再说吧。 
<img src ="http://www.cppblog.com/vczh/aggbug/118829.html" width = "1" height = "1" /><br><br><div align=right><a style="text-decoration:none;" href="http://www.cppblog.com/vczh/" target="_blank">陈梓瀚(vczh)</a> 2010-06-27 20:19 <a href="http://www.cppblog.com/vczh/archive/2010/06/27/118829.html#Feedback" target="_blank" style="text-decoration:none;">发表评论</a></div>]]></description></item><item><title>C++实用技巧（三）</title><link>http://www.cppblog.com/vczh/archive/2010/06/24/118635.html</link><dc:creator>陈梓瀚(vczh)</dc:creator><author>陈梓瀚(vczh)</author><pubDate>Thu, 24 Jun 2010 07:03:00 GMT</pubDate><guid>http://www.cppblog.com/vczh/archive/2010/06/24/118635.html</guid><wfw:comment>http://www.cppblog.com/vczh/comments/118635.html</wfw:comment><comments>http://www.cppblog.com/vczh/archive/2010/06/24/118635.html#Feedback</comments><slash:comments>14</slash:comments><wfw:commentRss>http://www.cppblog.com/vczh/comments/commentRss/118635.html</wfw:commentRss><trackback:ping>http://www.cppblog.com/vczh/services/trackbacks/118635.html</trackback:ping><description><![CDATA[<p>&nbsp;&nbsp;&nbsp; 复杂的东西写多了，如今写点简单的好了。由于功能上的需要，<a style="TEXT-DECORATION: underline" href="http://vlpp.codeplex.com/" target=_blank>Vczh Library++3.0</a>被我搞得很离谱。为了开发维护的遍历、减少粗心犯下的错误以及增强单元测试、回归测试和测试工具，因此记录下一些开发上的小技巧，以便抛砖引玉，造福他人。欢迎高手来喷，菜鸟膜拜。<br><br>&nbsp;&nbsp;&nbsp; 今天是关于内存的最后一篇了。<a style="TEXT-DECORATION: underline" href="http://www.cppblog.com/vczh/archive/2010/06/24/118603.html" target=_blank>上一篇文章</a>讲了为什么不能对一个东西随便memset。里面的demo代码出了点小bug，不过我不喜欢在发文章的时候里面的demo代码也拿去编译和运行，所以大家有什么发现的问题就评论吧。这样也便于后来的人不会受到误导。这次说的仍然是构造函数和析构函数的事情，不过我们将通过亲手开发一个智能指针的方法，知道引用计数如何帮助管理资源，以及错误使用引用计数的情况。<br><br>&nbsp;&nbsp;&nbsp; 首先先来看一下智能指针是如何帮助我们管理内存的。现在智能指针的实现非常多，我就假设这个类型叫Ptr&lt;T&gt;吧。这跟Vczh Library++ 3.0所使用的实现一样。</p>
<div style="BORDER-RIGHT: #cccccc 1px solid; PADDING-RIGHT: 5px; BORDER-TOP: #cccccc 1px solid; PADDING-LEFT: 4px; FONT-SIZE: 13px; PADDING-BOTTOM: 4px; BORDER-LEFT: #cccccc 1px solid; WIDTH: 98%; WORD-BREAK: break-all; PADDING-TOP: 4px; BORDER-BOTTOM: #cccccc 1px solid; BACKGROUND-COLOR: #eeeeee"><span style="COLOR: #008080">&nbsp;1</span>&nbsp;<span style="COLOR: #0000ff">class</span><span style="COLOR: #000000">&nbsp;Base<br></span><span style="COLOR: #008080">&nbsp;2</span>&nbsp;<span style="COLOR: #000000">{<br></span><span style="COLOR: #008080">&nbsp;3</span>&nbsp;<span style="COLOR: #000000"></span><span style="COLOR: #0000ff">public</span><span style="COLOR: #000000">:<br></span><span style="COLOR: #008080">&nbsp;4</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;</span><span style="COLOR: #0000ff">virtual</span><span style="COLOR: #000000">&nbsp;</span><span style="COLOR: #000000">~</span><span style="COLOR: #000000">Base(){}<br></span><span style="COLOR: #008080">&nbsp;5</span>&nbsp;<span style="COLOR: #000000">};<br></span><span style="COLOR: #008080">&nbsp;6</span>&nbsp;<span style="COLOR: #000000"><br></span><span style="COLOR: #008080">&nbsp;7</span>&nbsp;<span style="COLOR: #000000"></span><span style="COLOR: #0000ff">class</span><span style="COLOR: #000000">&nbsp;Derived1&nbsp;:&nbsp;</span><span style="COLOR: #0000ff">public</span><span style="COLOR: #000000">&nbsp;Base<br></span><span style="COLOR: #008080">&nbsp;8</span>&nbsp;<span style="COLOR: #000000">{<br></span><span style="COLOR: #008080">&nbsp;9</span>&nbsp;<span style="COLOR: #000000">};<br></span><span style="COLOR: #008080">10</span>&nbsp;<span style="COLOR: #000000"><br></span><span style="COLOR: #008080">11</span>&nbsp;<span style="COLOR: #000000"></span><span style="COLOR: #0000ff">class</span><span style="COLOR: #000000">&nbsp;Derived2&nbsp;:&nbsp;</span><span style="COLOR: #0000ff">public</span><span style="COLOR: #000000">&nbsp;Base<br></span><span style="COLOR: #008080">12</span>&nbsp;<span style="COLOR: #000000">{<br></span><span style="COLOR: #008080">13</span>&nbsp;<span style="COLOR: #000000">};<br></span><span style="COLOR: #008080">14</span>&nbsp;<span style="COLOR: #000000"><br></span><span style="COLOR: #008080">15</span>&nbsp;<span style="COLOR: #000000"></span><span style="COLOR: #008000">//</span><span style="COLOR: #008000">---------------------------------------</span><span style="COLOR: #008000"><br></span><span style="COLOR: #008080">16</span>&nbsp;<span style="COLOR: #008000"></span><span style="COLOR: #000000"><br></span><span style="COLOR: #008080">17</span>&nbsp;<span style="COLOR: #000000">List</span><span style="COLOR: #000000">&lt;</span><span style="COLOR: #000000">Ptr</span><span style="COLOR: #000000">&lt;</span><span style="COLOR: #000000">Base</span><span style="COLOR: #000000">&gt;&gt;</span><span style="COLOR: #000000">&nbsp;objects;<br></span><span style="COLOR: #008080">18</span>&nbsp;<span style="COLOR: #000000">objects.Add(</span><span style="COLOR: #0000ff">new</span><span style="COLOR: #000000">&nbsp;Derived1);<br></span><span style="COLOR: #008080">19</span>&nbsp;<span style="COLOR: #000000">objects.Add(</span><span style="COLOR: #0000ff">new</span><span style="COLOR: #000000">&nbsp;Derived2);<br></span><span style="COLOR: #008080">20</span>&nbsp;<span style="COLOR: #000000"><br></span><span style="COLOR: #008080">21</span>&nbsp;<span style="COLOR: #000000">List</span><span style="COLOR: #000000">&lt;</span><span style="COLOR: #000000">Ptr</span><span style="COLOR: #000000">&lt;</span><span style="COLOR: #000000">Base</span><span style="COLOR: #000000">&gt;&gt;</span><span style="COLOR: #000000">&nbsp;objects2;<br></span><span style="COLOR: #008080">22</span>&nbsp;<span style="COLOR: #000000">objects2.Add(objects[</span><span style="COLOR: #000000">0</span><span style="COLOR: #000000">]);</span></div>
<br>&nbsp;&nbsp;&nbsp; 当然这里的List也是Vczh Library++3.0实现的，不过这玩意儿跟vector也好跟C#的List也好都是一个概念，因此也就不需要多加解释了。我们可以看到智能指针的一个好处，只要没有循环引用出现，你无论怎么复制它，最终总是可以被析构掉的。另一个例子告诉我们智能指针如何处理类型转换：<br>
<div style="BORDER-RIGHT: #cccccc 1px solid; PADDING-RIGHT: 5px; BORDER-TOP: #cccccc 1px solid; PADDING-LEFT: 4px; FONT-SIZE: 13px; PADDING-BOTTOM: 4px; BORDER-LEFT: #cccccc 1px solid; WIDTH: 98%; WORD-BREAK: break-all; PADDING-TOP: 4px; BORDER-BOTTOM: #cccccc 1px solid; BACKGROUND-COLOR: #eeeeee"><span style="COLOR: #008080">1</span>&nbsp;<span style="COLOR: #000000">Ptr</span><span style="COLOR: #000000">&lt;</span><span style="COLOR: #000000">Derived1</span><span style="COLOR: #000000">&gt;</span><span style="COLOR: #000000">&nbsp;d1</span><span style="COLOR: #000000">=</span><span style="COLOR: #0000ff">new</span><span style="COLOR: #000000">&nbsp;Derived1;<br></span><span style="COLOR: #008080">2</span>&nbsp;<span style="COLOR: #000000">Ptr</span><span style="COLOR: #000000">&lt;</span><span style="COLOR: #000000">Base</span><span style="COLOR: #000000">&gt;</span><span style="COLOR: #000000">&nbsp;b</span><span style="COLOR: #000000">=</span><span style="COLOR: #000000">d1;<br></span><span style="COLOR: #008080">3</span>&nbsp;<span style="COLOR: #000000">Ptr</span><span style="COLOR: #000000">&lt;</span><span style="COLOR: #000000">Derived2</span><span style="COLOR: #000000">&gt;</span><span style="COLOR: #000000">&nbsp;d2</span><span style="COLOR: #000000">=</span><span style="COLOR: #000000">b.Cast</span><span style="COLOR: #000000">&lt;</span><span style="COLOR: #000000">Derived2</span><span style="COLOR: #000000">&gt;</span><span style="COLOR: #000000">();<br></span><span style="COLOR: #008080">4</span>&nbsp;<span style="COLOR: #000000"></span><span style="COLOR: #008000">//</span><span style="COLOR: #008000">&nbsp;d2是空，因为b指向的是Derived1而不是Derived2。</span></div>
<br>&nbsp;&nbsp;&nbsp; 这就如同我们Derived1*可以隐式转换到Base*，而当你使用dynamic_cast&lt;Derived2*&gt;(static_cast&lt;Base*&gt;(new Derived1))会得到0一样。智能指针在帮助我们析构对象的同时，也要做好类型转换的工作。<br><br>&nbsp;&nbsp;&nbsp; 好了，现在先让我们一步一步做出那个Ptr&lt;T&gt;。我们需要清楚这个智能指针所要实现的功能是什么，然后我们一个一个来做。首先让我们列出一张表：<br>&nbsp;&nbsp;&nbsp; 1、没有参数构造的时候，初始化为空<br>&nbsp;&nbsp;&nbsp; 2、使用指针构造的时候，拥有那个指针，并且在没有任何智能指针指向那个指针的时候删除掉该指针。<br>&nbsp;&nbsp;&nbsp; 3、智能指针进行复制的时候，两个智能指针共同拥有该内部指针。<br>&nbsp;&nbsp;&nbsp; 4、智能指针可以使用新的智能指针或裸指针重新赋值。<br>&nbsp;&nbsp;&nbsp; 5、需要支持隐式指针类型转换，static_cast不支持而dynamic_cast支持的转换则使用Cast&lt;T2&gt;()成员函数来解决。<br>&nbsp;&nbsp;&nbsp; 6、如果一个裸指针直接用来创建两个智能指针的话，期望的情况是当两个智能指针析构掉的时候，该指针会被delete两次从而崩溃。<br>&nbsp;&nbsp;&nbsp; 7、不处理循环引用。<br><br>&nbsp;&nbsp;&nbsp; 最后两点实际上是错误使用智能指针的最常见的两种情况。我们从1到5一个一个实现。首先是1。智能指针可以隐式转换成bool，可以通过operator-&gt;()拿到内部的T*。在没有使用参数构造的时候，需要转换成false，以及拿到0：<br>
<div style="BORDER-RIGHT: #cccccc 1px solid; PADDING-RIGHT: 5px; BORDER-TOP: #cccccc 1px solid; PADDING-LEFT: 4px; FONT-SIZE: 13px; PADDING-BOTTOM: 4px; BORDER-LEFT: #cccccc 1px solid; WIDTH: 98%; WORD-BREAK: break-all; PADDING-TOP: 4px; BORDER-BOTTOM: #cccccc 1px solid; BACKGROUND-COLOR: #eeeeee"><span style="COLOR: #008080">&nbsp;1</span>&nbsp;<span style="COLOR: #000000">template</span><span style="COLOR: #000000">&lt;</span><span style="COLOR: #000000">typename&nbsp;T</span><span style="COLOR: #000000">&gt;</span><span style="COLOR: #000000"><br></span><span style="COLOR: #008080">&nbsp;2</span>&nbsp;<span style="COLOR: #000000"></span><span style="COLOR: #0000ff">class</span><span style="COLOR: #000000">&nbsp;Ptr<br></span><span style="COLOR: #008080">&nbsp;3</span>&nbsp;<span style="COLOR: #000000">{<br></span><span style="COLOR: #008080">&nbsp;4</span>&nbsp;<span style="COLOR: #000000"></span><span style="COLOR: #0000ff">private</span><span style="COLOR: #000000">:<br></span><span style="COLOR: #008080">&nbsp;5</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;T</span><span style="COLOR: #000000">*</span><span style="COLOR: #000000">&nbsp;pointer;<br></span><span style="COLOR: #008080">&nbsp;6</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;</span><span style="COLOR: #0000ff">int</span><span style="COLOR: #000000">*</span><span style="COLOR: #000000">&nbsp;counter;<br></span><span style="COLOR: #008080">&nbsp;7</span>&nbsp;<span style="COLOR: #000000"><br></span><span style="COLOR: #008080">&nbsp;8</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;</span><span style="COLOR: #0000ff">void</span><span style="COLOR: #000000">&nbsp;Increase()<br></span><span style="COLOR: #008080">&nbsp;9</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;{<br></span><span style="COLOR: #008080">10</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;</span><span style="COLOR: #0000ff">if</span><span style="COLOR: #000000">(counter)</span><span style="COLOR: #000000">++*</span><span style="COLOR: #000000">counter;<br></span><span style="COLOR: #008080">11</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;}<br></span><span style="COLOR: #008080">12</span>&nbsp;<span style="COLOR: #000000"><br></span><span style="COLOR: #008080">13</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;</span><span style="COLOR: #0000ff">void</span><span style="COLOR: #000000">&nbsp;Decrease()<br></span><span style="COLOR: #008080">14</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;{<br></span><span style="COLOR: #008080">15</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;</span><span style="COLOR: #0000ff">if</span><span style="COLOR: #000000">(counter&nbsp;</span><span style="COLOR: #000000">&amp;&amp;</span><span style="COLOR: #000000">&nbsp;</span><span style="COLOR: #000000">--*</span><span style="COLOR: #000000">counter</span><span style="COLOR: #000000">==</span><span style="COLOR: #000000">0</span><span style="COLOR: #000000">)<br></span><span style="COLOR: #008080">16</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;{<br></span><span style="COLOR: #008080">17</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;delete&nbsp;counter;<br></span><span style="COLOR: #008080">18</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;delete&nbsp;pointer;<br></span><span style="COLOR: #008080">19</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;counter</span><span style="COLOR: #000000">=</span><span style="COLOR: #000000">0</span><span style="COLOR: #000000">;<br></span><span style="COLOR: #008080">20</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;pointer</span><span style="COLOR: #000000">=</span><span style="COLOR: #000000">0</span><span style="COLOR: #000000">;<br></span><span style="COLOR: #008080">21</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;}<br></span><span style="COLOR: #008080">22</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;}<br></span><span style="COLOR: #008080">23</span>&nbsp;<span style="COLOR: #000000"><br></span><span style="COLOR: #008080">24</span>&nbsp;<span style="COLOR: #000000"></span><span style="COLOR: #0000ff">public</span><span style="COLOR: #000000">:<br></span><span style="COLOR: #008080">25</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;Ptr():pointer(</span><span style="COLOR: #000000">0</span><span style="COLOR: #000000">),counter(</span><span style="COLOR: #000000">0</span><span style="COLOR: #000000">)<br></span><span style="COLOR: #008080">26</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;{<br></span><span style="COLOR: #008080">27</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;}<br></span><span style="COLOR: #008080">28</span>&nbsp;<span style="COLOR: #000000"><br></span><span style="COLOR: #008080">29</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;</span><span style="COLOR: #000000">~</span><span style="COLOR: #000000">Ptr()<br></span><span style="COLOR: #008080">30</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;{<br></span><span style="COLOR: #008080">31</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;Decrease();<br></span><span style="COLOR: #008080">32</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;}<br></span><span style="COLOR: #008080">33</span>&nbsp;<span style="COLOR: #000000"><br></span><span style="COLOR: #008080">34</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;</span><span style="COLOR: #0000ff">operator</span><span style="COLOR: #000000">&nbsp;</span><span style="COLOR: #0000ff">bool</span><span style="COLOR: #000000">()</span><span style="COLOR: #0000ff">const</span><span style="COLOR: #000000"><br></span><span style="COLOR: #008080">35</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;{<br></span><span style="COLOR: #008080">36</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;</span><span style="COLOR: #0000ff">return</span><span style="COLOR: #000000">&nbsp;counter</span><span style="COLOR: #000000">!=</span><span style="COLOR: #000000">0</span><span style="COLOR: #000000">;<br></span><span style="COLOR: #008080">37</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;}<br></span><span style="COLOR: #008080">38</span>&nbsp;<span style="COLOR: #000000"><br></span><span style="COLOR: #008080">39</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;T</span><span style="COLOR: #000000">*</span><span style="COLOR: #000000">&nbsp;</span><span style="COLOR: #0000ff">operator</span><span style="COLOR: #000000">-&gt;</span><span style="COLOR: #000000">()</span><span style="COLOR: #0000ff">const</span><span style="COLOR: #000000"><br></span><span style="COLOR: #008080">40</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;{<br></span><span style="COLOR: #008080">41</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;</span><span style="COLOR: #0000ff">return</span><span style="COLOR: #000000">&nbsp;pointer;<br></span><span style="COLOR: #008080">42</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;}<br></span><span style="COLOR: #008080">43</span>&nbsp;<span style="COLOR: #000000">};</span></div>
<br>&nbsp;&nbsp;&nbsp; 在这里我们实现了构造函数和析构函数。构造函数把内部指针和引用计数的指针都初始化为空，而析构函数则进行引用计数的减一操作。另外两个操作符重载很容易理解。我们主要来看看Increase函数和Decrease函数都分别做了什么。Increase函数在引用计数存在的情况下，把引用计数加一。而Decrease函数在引用计数存在的情况下，把引用计数减一，如果引用计数在减一过程中变成了0，则删掉拥有的资源。<br><br>&nbsp;&nbsp;&nbsp; 当然到了这个时候智能指针还不能用，我们必须替他加上复制构造函数，operator=操作符重载以及使用指针赋值的情况。首先让我们来看使用指针赋值的话我们应该加上什么：<br>
<div style="BORDER-RIGHT: #cccccc 1px solid; PADDING-RIGHT: 5px; BORDER-TOP: #cccccc 1px solid; PADDING-LEFT: 4px; FONT-SIZE: 13px; PADDING-BOTTOM: 4px; BORDER-LEFT: #cccccc 1px solid; WIDTH: 98%; WORD-BREAK: break-all; PADDING-TOP: 4px; BORDER-BOTTOM: #cccccc 1px solid; BACKGROUND-COLOR: #eeeeee"><span style="COLOR: #008080">&nbsp;1</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;Ptr(T</span><span style="COLOR: #000000">*</span><span style="COLOR: #000000">&nbsp;p):pointer(</span><span style="COLOR: #000000">0</span><span style="COLOR: #000000">),counter(</span><span style="COLOR: #000000">0</span><span style="COLOR: #000000">)<br></span><span style="COLOR: #008080">&nbsp;2</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;{<br></span><span style="COLOR: #008080">&nbsp;3</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;</span><span style="COLOR: #000000">*</span><span style="COLOR: #0000ff">this</span><span style="COLOR: #000000">=</span><span style="COLOR: #000000">p;<br></span><span style="COLOR: #008080">&nbsp;4</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;}<br></span><span style="COLOR: #008080">&nbsp;5</span>&nbsp;<span style="COLOR: #000000"><br></span><span style="COLOR: #008080">&nbsp;6</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;Ptr</span><span style="COLOR: #000000">&lt;</span><span style="COLOR: #000000">T</span><span style="COLOR: #000000">&gt;&amp;</span><span style="COLOR: #000000">&nbsp;</span><span style="COLOR: #0000ff">operator</span><span style="COLOR: #000000">=</span><span style="COLOR: #000000">(T</span><span style="COLOR: #000000">*</span><span style="COLOR: #000000">&nbsp;p)<br></span><span style="COLOR: #008080">&nbsp;7</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;{<br></span><span style="COLOR: #008080">&nbsp;8</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;Decrease();<br></span><span style="COLOR: #008080">&nbsp;9</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;</span><span style="COLOR: #0000ff">if</span><span style="COLOR: #000000">(p)<br></span><span style="COLOR: #008080">10</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;{<br></span><span style="COLOR: #008080">11</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;pointer</span><span style="COLOR: #000000">=</span><span style="COLOR: #000000">p;<br></span><span style="COLOR: #008080">12</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;counter</span><span style="COLOR: #000000">=</span><span style="COLOR: #0000ff">new</span><span style="COLOR: #000000">&nbsp;</span><span style="COLOR: #0000ff">int</span><span style="COLOR: #000000">(</span><span style="COLOR: #000000">1</span><span style="COLOR: #000000">);<br></span><span style="COLOR: #008080">13</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;}<br></span><span style="COLOR: #008080">14</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;</span><span style="COLOR: #0000ff">else</span><span style="COLOR: #000000"><br></span><span style="COLOR: #008080">15</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;{<br></span><span style="COLOR: #008080">16</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;pointer</span><span style="COLOR: #000000">=</span><span style="COLOR: #000000">0</span><span style="COLOR: #000000">;<br></span><span style="COLOR: #008080">17</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;counter</span><span style="COLOR: #000000">=</span><span style="COLOR: #000000">0</span><span style="COLOR: #000000">;<br></span><span style="COLOR: #008080">18</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;}<br></span><span style="COLOR: #008080">19</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;</span><span style="COLOR: #0000ff">return</span><span style="COLOR: #000000">&nbsp;</span><span style="COLOR: #000000">*</span><span style="COLOR: #0000ff">this</span><span style="COLOR: #000000">;<br></span><span style="COLOR: #008080">20</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;}</span></div>
<br>&nbsp;&nbsp;&nbsp; 这里还是偷工减料了的，构造函数接受了指针的话，还是转给operator=去调用了。当一个智能指针被一个新指针赋值的时候，我们首先要减掉一个引用计数，因为原来的指针再也不被这个智能指针共享了。之后就进行判断，如果来的是0，那么就变成空。如果不是0，就拥有该指针，引用计数初始化成1。于是我们就可以这么使用了：<br>
<div style="BORDER-RIGHT: #cccccc 1px solid; PADDING-RIGHT: 5px; BORDER-TOP: #cccccc 1px solid; PADDING-LEFT: 4px; FONT-SIZE: 13px; PADDING-BOTTOM: 4px; BORDER-LEFT: #cccccc 1px solid; WIDTH: 98%; WORD-BREAK: break-all; PADDING-TOP: 4px; BORDER-BOTTOM: #cccccc 1px solid; BACKGROUND-COLOR: #eeeeee"><span style="COLOR: #008080">1</span>&nbsp;<span style="COLOR: #000000">Ptr</span><span style="COLOR: #000000">&lt;</span><span style="COLOR: #000000">Base</span><span style="COLOR: #000000">&gt;</span><span style="COLOR: #000000">&nbsp;b</span><span style="COLOR: #000000">=</span><span style="COLOR: #0000ff">new</span><span style="COLOR: #000000">&nbsp;Derived1;<br></span><span style="COLOR: #008080">2</span>&nbsp;<span style="COLOR: #000000">Ptr</span><span style="COLOR: #000000">&lt;</span><span style="COLOR: #000000">Derived2</span><span style="COLOR: #000000">&gt;</span><span style="COLOR: #000000">&nbsp;d2</span><span style="COLOR: #000000">=</span><span style="COLOR: #0000ff">new</span><span style="COLOR: #000000">&nbsp;Derived2;</span></div>
<br>&nbsp;&nbsp;&nbsp; 让我们开始复制他们吧。复制的要领是，先把之前拥有的指针脱离掉，然后连接到一个新的智能指针上面去。我们知道非空智能指针有多少个，总的引用计数的和就是多少，只是分配到各个指针上面的数字不一样而已：<br>
<div style="BORDER-RIGHT: #cccccc 1px solid; PADDING-RIGHT: 5px; BORDER-TOP: #cccccc 1px solid; PADDING-LEFT: 4px; FONT-SIZE: 13px; PADDING-BOTTOM: 4px; BORDER-LEFT: #cccccc 1px solid; WIDTH: 98%; WORD-BREAK: break-all; PADDING-TOP: 4px; BORDER-BOTTOM: #cccccc 1px solid; BACKGROUND-COLOR: #eeeeee"><span style="COLOR: #008080">&nbsp;1</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;Ptr(</span><span style="COLOR: #0000ff">const</span><span style="COLOR: #000000">&nbsp;Ptr</span><span style="COLOR: #000000">&lt;</span><span style="COLOR: #000000">T</span><span style="COLOR: #000000">&gt;&amp;</span><span style="COLOR: #000000">&nbsp;p):pointer(p.pointer),counter(p.counter)<br></span><span style="COLOR: #008080">&nbsp;2</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;{<br></span><span style="COLOR: #008080">&nbsp;3</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;Increase();<br></span><span style="COLOR: #008080">&nbsp;4</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;}<br></span><span style="COLOR: #008080">&nbsp;5</span>&nbsp;<span style="COLOR: #000000"><br></span><span style="COLOR: #008080">&nbsp;6</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;Ptr</span><span style="COLOR: #000000">&lt;</span><span style="COLOR: #000000">T</span><span style="COLOR: #000000">&gt;&amp;</span><span style="COLOR: #000000">&nbsp;</span><span style="COLOR: #0000ff">operator</span><span style="COLOR: #000000">=</span><span style="COLOR: #000000">(</span><span style="COLOR: #0000ff">const</span><span style="COLOR: #000000">&nbsp;Ptr</span><span style="COLOR: #000000">&lt;</span><span style="COLOR: #000000">T</span><span style="COLOR: #000000">&gt;&amp;</span><span style="COLOR: #000000">&nbsp;p)<br></span><span style="COLOR: #008080">&nbsp;7</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;{<br></span><span style="COLOR: #008080">&nbsp;8</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;</span><span style="COLOR: #0000ff">if</span><span style="COLOR: #000000">(</span><span style="COLOR: #0000ff">this</span><span style="COLOR: #000000">!=&amp;</span><span style="COLOR: #000000">p)<br></span><span style="COLOR: #008080">&nbsp;9</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;{<br></span><span style="COLOR: #008080">10</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Decrease();<br></span><span style="COLOR: #008080">11</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;pointer</span><span style="COLOR: #000000">=</span><span style="COLOR: #000000">p.pointer;<br></span><span style="COLOR: #008080">12</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;counter</span><span style="COLOR: #000000">=</span><span style="COLOR: #000000">p.counter;<br></span><span style="COLOR: #008080">13</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Increase();<br></span><span style="COLOR: #008080">14</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;}<br></span><span style="COLOR: #008080">15</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;</span><span style="COLOR: #0000ff">return</span><span style="COLOR: #000000">&nbsp;</span><span style="COLOR: #000000">*</span><span style="COLOR: #0000ff">this</span><span style="COLOR: #000000">;<br></span><span style="COLOR: #008080">16</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;}</span></div>
<br>&nbsp;&nbsp;&nbsp; 在上一篇文章有朋友指出重载operator=的时候需要考虑是不是自己赋值给自己，其实这是很正确的。我们写每一类的时候，特别是当类拥有自己控制的资源的时候，需要非常注意这件事情。当然如果只是复制几个对象而不会new啊delete还是close什么handle，那检查不检查也无所谓了。在这里我们非常清楚，当增加一个新的非空智能指针的时候，引用计数的总和会加一。当修改一个非空智能指针的结果也是非空的时候，引用计数的和保持不变。当然这是应该的，因为我们需要在所有非空智能指针都被毁掉的时候，释放受保护的所有资源。<br><br>&nbsp;&nbsp;&nbsp; 到了这里一个智能指针基本上已经能用了，但是还不能处理父类子类的情况。这个是比较麻烦的，一个Ptr&lt;Derived&gt;事实上没有权限访问Ptr&lt;Base&gt;的内部对象。因此我们需要通过友元类来解决这个问题。现在让我们来添加两个新的函数吧，从一个任意的Ptr&lt;C&gt;复制到Ptr&lt;T&gt;，然后保证只有当C*可以隐式转换成T*的时候编译能够通过：<br>
<div style="BORDER-RIGHT: #cccccc 1px solid; PADDING-RIGHT: 5px; BORDER-TOP: #cccccc 1px solid; PADDING-LEFT: 4px; FONT-SIZE: 13px; PADDING-BOTTOM: 4px; BORDER-LEFT: #cccccc 1px solid; WIDTH: 98%; WORD-BREAK: break-all; PADDING-TOP: 4px; BORDER-BOTTOM: #cccccc 1px solid; BACKGROUND-COLOR: #eeeeee"><span style="COLOR: #008080">&nbsp;1</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;template</span><span style="COLOR: #000000">&lt;</span><span style="COLOR: #000000">X</span><span style="COLOR: #000000">&gt;</span><span style="COLOR: #000000">&nbsp;friend&nbsp;</span><span style="COLOR: #0000ff">class</span><span style="COLOR: #000000">&nbsp;Ptr;<br></span><span style="COLOR: #008080">&nbsp;2</span>&nbsp;<span style="COLOR: #000000"><br></span><span style="COLOR: #008080">&nbsp;3</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;template</span><span style="COLOR: #000000">&lt;</span><span style="COLOR: #000000">typename&nbsp;C</span><span style="COLOR: #000000">&gt;</span><span style="COLOR: #000000"><br></span><span style="COLOR: #008080">&nbsp;4</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;Ptr(</span><span style="COLOR: #0000ff">const</span><span style="COLOR: #000000">&nbsp;Ptr</span><span style="COLOR: #000000">&lt;</span><span style="COLOR: #000000">C</span><span style="COLOR: #000000">&gt;&amp;</span><span style="COLOR: #000000">&nbsp;p):pointer(p.pointer),counter(p.counter)<br></span><span style="COLOR: #008080">&nbsp;5</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;{<br></span><span style="COLOR: #008080">&nbsp;6</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;Increase();<br></span><span style="COLOR: #008080">&nbsp;7</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;}<br></span><span style="COLOR: #008080">&nbsp;8</span>&nbsp;<span style="COLOR: #000000"><br></span><span style="COLOR: #008080">&nbsp;9</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;template</span><span style="COLOR: #000000">&lt;</span><span style="COLOR: #000000">typename&nbsp;C</span><span style="COLOR: #000000">&gt;</span><span style="COLOR: #000000"><br></span><span style="COLOR: #008080">10</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;Ptr</span><span style="COLOR: #000000">&lt;</span><span style="COLOR: #000000">T</span><span style="COLOR: #000000">&gt;&amp;</span><span style="COLOR: #000000">&nbsp;</span><span style="COLOR: #0000ff">operator</span><span style="COLOR: #000000">=</span><span style="COLOR: #000000">(</span><span style="COLOR: #0000ff">const</span><span style="COLOR: #000000">&nbsp;Ptr</span><span style="COLOR: #000000">&lt;</span><span style="COLOR: #000000">C</span><span style="COLOR: #000000">&gt;&amp;</span><span style="COLOR: #000000">&nbsp;p)<br></span><span style="COLOR: #008080">11</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;{<br></span><span style="COLOR: #008080">12</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;Decrease();<br></span><span style="COLOR: #008080">13</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;pointer</span><span style="COLOR: #000000">=</span><span style="COLOR: #000000">p.pointer;<br></span><span style="COLOR: #008080">14</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;counter</span><span style="COLOR: #000000">=</span><span style="COLOR: #000000">p.counter;<br></span><span style="COLOR: #008080">15</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;Increase();<br></span><span style="COLOR: #008080">16</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;</span><span style="COLOR: #0000ff">return</span><span style="COLOR: #000000">&nbsp;</span><span style="COLOR: #000000">*</span><span style="COLOR: #0000ff">this</span><span style="COLOR: #000000">;<br></span><span style="COLOR: #008080">17</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;}</span></div>
<br>&nbsp;&nbsp;&nbsp; 注意这里我们的operator=并不用检查是不是自己给自己赋值，因为这是两个不同的类，相同的话会调用上面那个operator=的。如果C*不能隐式转换到T*的话，这里的pointer=p.pointer就会失败，从而满足了我们的要求。<br><br>&nbsp;&nbsp;&nbsp; 现在我们能够做的事情就更多了：<br>
<div style="BORDER-RIGHT: #cccccc 1px solid; PADDING-RIGHT: 5px; BORDER-TOP: #cccccc 1px solid; PADDING-LEFT: 4px; FONT-SIZE: 13px; PADDING-BOTTOM: 4px; BORDER-LEFT: #cccccc 1px solid; WIDTH: 98%; WORD-BREAK: break-all; PADDING-TOP: 4px; BORDER-BOTTOM: #cccccc 1px solid; BACKGROUND-COLOR: #eeeeee"><span style="COLOR: #008080">1</span>&nbsp;<span style="COLOR: #000000">Ptr</span><span style="COLOR: #000000">&lt;</span><span style="COLOR: #000000">Derived1</span><span style="COLOR: #000000">&gt;</span><span style="COLOR: #000000">&nbsp;d1</span><span style="COLOR: #000000">=</span><span style="COLOR: #0000ff">new</span><span style="COLOR: #000000">&nbsp;Derived1;<br></span><span style="COLOR: #008080">2</span>&nbsp;<span style="COLOR: #000000">Ptr</span><span style="COLOR: #000000">&lt;</span><span style="COLOR: #000000">Base</span><span style="COLOR: #000000">&gt;</span><span style="COLOR: #000000">&nbsp;b</span><span style="COLOR: #000000">=</span><span style="COLOR: #000000">d1;</span></div>
<br>&nbsp;&nbsp;&nbsp; 于是我们只剩下最后一个Cast函数了。这个函数内部使用dynamic_cast来做判断，如果转换失败，会返回空指针：<br>
<div style="BORDER-RIGHT: #cccccc 1px solid; PADDING-RIGHT: 5px; BORDER-TOP: #cccccc 1px solid; PADDING-LEFT: 4px; FONT-SIZE: 13px; PADDING-BOTTOM: 4px; BORDER-LEFT: #cccccc 1px solid; WIDTH: 98%; WORD-BREAK: break-all; PADDING-TOP: 4px; BORDER-BOTTOM: #cccccc 1px solid; BACKGROUND-COLOR: #eeeeee"><span style="COLOR: #008080">&nbsp;1</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;tempalte</span><span style="COLOR: #000000">&lt;</span><span style="COLOR: #000000">typename&nbsp;C</span><span style="COLOR: #000000">&gt;</span><span style="COLOR: #000000"><br></span><span style="COLOR: #008080">&nbsp;2</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;Ptr</span><span style="COLOR: #000000">&lt;</span><span style="COLOR: #000000">C</span><span style="COLOR: #000000">&gt;</span><span style="COLOR: #000000">&nbsp;Cast()</span><span style="COLOR: #0000ff">const</span><span style="COLOR: #000000"><br></span><span style="COLOR: #008080">&nbsp;3</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;{<br></span><span style="COLOR: #008080">&nbsp;4</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;C</span><span style="COLOR: #000000">*</span><span style="COLOR: #000000">&nbsp;converted</span><span style="COLOR: #000000">=</span><span style="COLOR: #000000">dynamic_cast</span><span style="COLOR: #000000">&lt;</span><span style="COLOR: #000000">C</span><span style="COLOR: #000000">*&gt;</span><span style="COLOR: #000000">(pointer);<br></span><span style="COLOR: #008080">&nbsp;5</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;Ptr</span><span style="COLOR: #000000">&lt;</span><span style="COLOR: #000000">C</span><span style="COLOR: #000000">&gt;</span><span style="COLOR: #000000">&nbsp;result;<br></span><span style="COLOR: #008080">&nbsp;6</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;</span><span style="COLOR: #0000ff">if</span><span style="COLOR: #000000">(converted)<br></span><span style="COLOR: #008080">&nbsp;7</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;{<br></span><span style="COLOR: #008080">&nbsp;8</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;result.pointer</span><span style="COLOR: #000000">=</span><span style="COLOR: #000000">converted;<br></span><span style="COLOR: #008080">&nbsp;9</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;result.counter</span><span style="COLOR: #000000">=</span><span style="COLOR: #000000">counter;<br></span><span style="COLOR: #008080">10</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Increase();<br></span><span style="COLOR: #008080">11</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;}<br></span><span style="COLOR: #008080">12</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;</span><span style="COLOR: #0000ff">return</span><span style="COLOR: #000000">&nbsp;result;<br></span><span style="COLOR: #008080">13</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;}</span></div>
<br>&nbsp;&nbsp;&nbsp; 这是一种hack的方法，平时是不鼓励的&#8230;&#8230;不过因为操作的都是Ptr，而且特化Ptr也是使用错误的一种，所以这里就不管了。我们会检查dynamic_cast的结果，如果成功了，那么会返回一个非空的新智能指针，而且这个时候我们也要记住Increase一下。<br><br>&nbsp;&nbsp;&nbsp; 好了，基本功能就完成了。当然一个智能指针还要很多其他功能，譬如说比较什么的，这个就你们自己搞定哈。<br><br>&nbsp;&nbsp;&nbsp; 指针和内存就说到这里了，下一篇讲如何利用一个好的IDE构造轻量级单元测试系统。我们都说好的工具能够提高生产力，因此这种方法不能脱离一个好的IDE使用。
<img src ="http://www.cppblog.com/vczh/aggbug/118635.html" width = "1" height = "1" /><br><br><div align=right><a style="text-decoration:none;" href="http://www.cppblog.com/vczh/" target="_blank">陈梓瀚(vczh)</a> 2010-06-24 15:03 <a href="http://www.cppblog.com/vczh/archive/2010/06/24/118635.html#Feedback" target="_blank" style="text-decoration:none;">发表评论</a></div>]]></description></item><item><title>C++实用技巧（二）</title><link>http://www.cppblog.com/vczh/archive/2010/06/24/118603.html</link><dc:creator>陈梓瀚(vczh)</dc:creator><author>陈梓瀚(vczh)</author><pubDate>Wed, 23 Jun 2010 18:12:00 GMT</pubDate><guid>http://www.cppblog.com/vczh/archive/2010/06/24/118603.html</guid><wfw:comment>http://www.cppblog.com/vczh/comments/118603.html</wfw:comment><comments>http://www.cppblog.com/vczh/archive/2010/06/24/118603.html#Feedback</comments><slash:comments>23</slash:comments><wfw:commentRss>http://www.cppblog.com/vczh/comments/commentRss/118603.html</wfw:commentRss><trackback:ping>http://www.cppblog.com/vczh/services/trackbacks/118603.html</trackback:ping><description><![CDATA[&nbsp;&nbsp;&nbsp; 复杂的东西写多了，如今写点简单的好了。由于功能上的需要，<a style="TEXT-DECORATION: underline" href="http://vlpp.codeplex.com/" target=_blank>Vczh Library++3.0</a>被我搞得很离谱。为了开发维护的遍历、减少粗心犯下的错误以及增强单元测试、回归测试和测试工具，因此记录下一些开发上的小技巧，以便抛砖引玉，造福他人。欢迎高手来喷，菜鸟膜拜。<br><br>&nbsp;&nbsp;&nbsp; <a style="TEXT-DECORATION: underline" href="http://www.cppblog.com/vczh/archive/2010/06/24/118493.html" target=_blank>上一篇文章</a>讲到了如何检查内存泄露。其实只要肯用C++的STL里面的高级功能的话，内存泄露是很容易避免的。我在开发Vczh Library++ 3.0的时候，所有的测试用例都保证跑完了没有内存泄露。但是很可惜有些C++团队不能使用异常，更甚者不允许写构造函数析构函数之类，前一个还好，后一个简直就是在用C。当然有这些变态规定的地方STL都是用不了的，所以我们更加需要扎实的基础来开发C++程序。<br><br>&nbsp;&nbsp;&nbsp; 今天这一篇主要还是讲指针的问题。因为上一篇文章一笔带过，今天就来详细讲内存泄漏或者野指针发生的各种情况。当然我不可能一下子举出全部的例子，只能说一些常见的。<br><br>&nbsp;&nbsp;&nbsp; <strong>一、错误覆盖内存。<br></strong><br>&nbsp;&nbsp;&nbsp; 之前提到的不能随便乱memset其实就是为了避免这个问题的。其实memcpy也不能乱用，我们来看一个例子，最简单的：<br>
<div style="BORDER-BOTTOM: #cccccc 1px solid; BORDER-LEFT: #cccccc 1px solid; PADDING-BOTTOM: 4px; BACKGROUND-COLOR: #eeeeee; PADDING-LEFT: 4px; WIDTH: 98%; PADDING-RIGHT: 5px; FONT-SIZE: 13px; WORD-BREAK: break-all; BORDER-TOP: #cccccc 1px solid; BORDER-RIGHT: #cccccc 1px solid; PADDING-TOP: 4px"><span style="COLOR: #008080">&nbsp;1</span>&nbsp;<span style="COLOR: #0000ff">#define</span><span style="COLOR: #000000">&nbsp;MAX_STRING&nbsp;20;</span><span style="COLOR: #000000"><br></span><span style="COLOR: #008080">&nbsp;2</span>&nbsp;<span style="COLOR: #000000"><br></span><span style="COLOR: #008080">&nbsp;3</span>&nbsp;<span style="COLOR: #000000"></span><span style="COLOR: #0000ff">struct</span><span style="COLOR: #000000">&nbsp;Student<br></span><span style="COLOR: #008080">&nbsp;4</span>&nbsp;<span style="COLOR: #000000">{<br></span><span style="COLOR: #008080">&nbsp;5</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;</span><span style="COLOR: #0000ff">char</span><span style="COLOR: #000000">&nbsp;name[MAX_STRING];<br></span><span style="COLOR: #008080">&nbsp;6</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;</span><span style="COLOR: #0000ff">char</span><span style="COLOR: #000000">&nbsp;id[MAX_STRING];<br></span><span style="COLOR: #008080">&nbsp;7</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;</span><span style="COLOR: #0000ff">int</span><span style="COLOR: #000000">&nbsp;chinese;<br></span><span style="COLOR: #008080">&nbsp;8</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;</span><span style="COLOR: #0000ff">int</span><span style="COLOR: #000000">&nbsp;math;<br></span><span style="COLOR: #008080">&nbsp;9</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;</span><span style="COLOR: #0000ff">int</span><span style="COLOR: #000000">&nbsp;english;<br></span><span style="COLOR: #008080">10</span>&nbsp;<span style="COLOR: #000000">};</span></div>
<br>&nbsp;&nbsp;&nbsp; 大家对这种结构肯定十分熟悉，毕竟是大学时候经常要写的作业题&#8230;&#8230;好了，大家很容易看得出来这其实是C语言的经典写法。我们拿到手之后，一般会先初始化一下，然后赋值。<br>
<div style="BORDER-BOTTOM: #cccccc 1px solid; BORDER-LEFT: #cccccc 1px solid; PADDING-BOTTOM: 4px; BACKGROUND-COLOR: #eeeeee; PADDING-LEFT: 4px; WIDTH: 98%; PADDING-RIGHT: 5px; FONT-SIZE: 13px; WORD-BREAK: break-all; BORDER-TOP: #cccccc 1px solid; BORDER-RIGHT: #cccccc 1px solid; PADDING-TOP: 4px"><span style="COLOR: #008080">1</span>&nbsp;<span style="COLOR: #000000">Student&nbsp;vczh;<br></span><span style="COLOR: #008080">2</span>&nbsp;<span style="COLOR: #000000">memset(</span><span style="COLOR: #000000">&amp;</span><span style="COLOR: #000000">vczh,&nbsp;</span><span style="COLOR: #000000">0</span><span style="COLOR: #000000">,&nbsp;</span><span style="COLOR: #0000ff">sizeof</span><span style="COLOR: #000000">(vczh));<br></span><span style="COLOR: #008080">3</span>&nbsp;<span style="COLOR: #000000">strcpy(vczh.name,&nbsp;</span><span style="COLOR: #000000">"</span><span style="COLOR: #000000">vczh</span><span style="COLOR: #000000">"</span><span style="COLOR: #000000">);<br></span><span style="COLOR: #008080">4</span>&nbsp;<span style="COLOR: #000000">strcpy(vczh.id,&nbsp;</span><span style="COLOR: #000000">"</span><span style="COLOR: #000000">VCZH'S&nbsp;ID</span><span style="COLOR: #000000">"</span><span style="COLOR: #000000">);<br></span><span style="COLOR: #008080">5</span>&nbsp;<span style="COLOR: #000000">vczh.chinese</span><span style="COLOR: #000000">=</span><span style="COLOR: #000000">70</span><span style="COLOR: #000000">;<br></span><span style="COLOR: #008080">6</span>&nbsp;<span style="COLOR: #000000">vczh.math</span><span style="COLOR: #000000">=</span><span style="COLOR: #000000">90</span><span style="COLOR: #000000">;<br></span><span style="COLOR: #008080">7</span>&nbsp;<span style="COLOR: #000000">vczh.english</span><span style="COLOR: #000000">=</span><span style="COLOR: #000000">80</span><span style="COLOR: #000000">;</span></div>
<br>&nbsp;&nbsp;&nbsp; 为什么要在这里使用memset呢？memset的用处是将一段内存的每一个字节都设置成同一个数字。这里是0，因此两个字符串成员的所有字节都会变成0。因此在memset了Student之后，我们通过正常方法来访问name和id的时候都会得到空串。而且如果Student里面有指针的话，0指针代表的是没有指向任何有效对象，因此这个时候对指针指向的对象进行读写就会立刻崩溃。对于其他数值，0一般作为初始值也不会有什么问题（double什么的要小心）。这就是我们写程序的时候使用memset的原因。<br><br>&nbsp;&nbsp;&nbsp; 好了，如今社会进步，人民当家做主了，死程们再也不需要受到可恶的C语言剥削了，我们可以使用C++！因此我们借助STL的力量把Student改写成下面这种带有C++味道的形式：<br>
<div style="BORDER-BOTTOM: #cccccc 1px solid; BORDER-LEFT: #cccccc 1px solid; PADDING-BOTTOM: 4px; BACKGROUND-COLOR: #eeeeee; PADDING-LEFT: 4px; WIDTH: 98%; PADDING-RIGHT: 5px; FONT-SIZE: 13px; WORD-BREAK: break-all; BORDER-TOP: #cccccc 1px solid; BORDER-RIGHT: #cccccc 1px solid; PADDING-TOP: 4px"><span style="COLOR: #008080">1</span>&nbsp;<span style="COLOR: #0000ff">struct</span><span style="COLOR: #000000">&nbsp;Student<br></span><span style="COLOR: #008080">2</span>&nbsp;<span style="COLOR: #000000">{<br></span><span style="COLOR: #008080">3</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;std::</span><span style="COLOR: #0000ff">string</span><span style="COLOR: #000000">&nbsp;name;<br></span><span style="COLOR: #008080">4</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;std::</span><span style="COLOR: #0000ff">string</span><span style="COLOR: #000000">&nbsp;id;<br></span><span style="COLOR: #008080">5</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;</span><span style="COLOR: #0000ff">int</span><span style="COLOR: #000000">&nbsp;chinese;<br></span><span style="COLOR: #008080">6</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;</span><span style="COLOR: #0000ff">int</span><span style="COLOR: #000000">&nbsp;math;<br></span><span style="COLOR: #008080">7</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;</span><span style="COLOR: #0000ff">int</span><span style="COLOR: #000000">&nbsp;english;<br></span><span style="COLOR: #008080">8</span>&nbsp;<span style="COLOR: #000000">};</span></div>
<br>&nbsp;&nbsp;&nbsp; 我们仍然需要对Student进行初始化，不然三个分数还是随机值。但是我们又不想每一次创建的时候都对他们分别进行赋值初始化城0。这个时候你心里可能还是想着memset，<span style="COLOR: red"><strong>这就错了</strong></span>！在memset的时候，你会把std::string内部的不知道什么东西也给memset掉。假如一个空的std::string里面存放的指针指向的是一个空的字符串而不是用0来代表空的时候，一下子内部的指针就被你刷成0，等下std::string的析构函数就没办法delete掉指针了，于是<span style="COLOR: red"><strong>内存泄露就出现了</strong></span>。有些朋友可能不知道上面那句话说的是什么意思，我们现在来模拟一下不能memset的std::string要怎么实现。<br><br>&nbsp;&nbsp;&nbsp; 为了让memset一定出现内存泄露，那么std::string里面的指针必须永远都指向一个有效的东西。当然我们还需要在字符串进行复制的时候复制指针。我们这里不考虑各种优化技术，用最简单的方法做一个字符串出来：<br>
<div style="BORDER-BOTTOM: #cccccc 1px solid; BORDER-LEFT: #cccccc 1px solid; PADDING-BOTTOM: 4px; BACKGROUND-COLOR: #eeeeee; PADDING-LEFT: 4px; WIDTH: 98%; PADDING-RIGHT: 5px; FONT-SIZE: 13px; WORD-BREAK: break-all; BORDER-TOP: #cccccc 1px solid; BORDER-RIGHT: #cccccc 1px solid; PADDING-TOP: 4px"><span style="COLOR: #008080">&nbsp;1</span>&nbsp;<span style="COLOR: #0000ff">class</span><span style="COLOR: #000000">&nbsp;String<br></span><span style="COLOR: #008080">&nbsp;2</span>&nbsp;<span style="COLOR: #000000">{<br></span><span style="COLOR: #008080">&nbsp;3</span>&nbsp;<span style="COLOR: #000000"></span><span style="COLOR: #0000ff">private</span><span style="COLOR: #000000">:<br></span><span style="COLOR: #008080">&nbsp;4</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;</span><span style="COLOR: #0000ff">char</span><span style="COLOR: #000000">*</span><span style="COLOR: #000000">&nbsp;buffer;<br></span><span style="COLOR: #008080">&nbsp;5</span>&nbsp;<span style="COLOR: #000000"><br></span><span style="COLOR: #008080">&nbsp;6</span>&nbsp;<span style="COLOR: #000000"></span><span style="COLOR: #0000ff">public</span><span style="COLOR: #000000">:<br></span><span style="COLOR: #008080">&nbsp;7</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;String()<br></span><span style="COLOR: #008080">&nbsp;8</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;{<br></span><span style="COLOR: #008080">&nbsp;9</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;buffer</span><span style="COLOR: #000000">=</span><span style="COLOR: #0000ff">new</span><span style="COLOR: #000000">&nbsp;</span><span style="COLOR: #0000ff">char</span><span style="COLOR: #000000">[</span><span style="COLOR: #000000">1</span><span style="COLOR: #000000">];<br></span><span style="COLOR: #008080">10</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;buffer[</span><span style="COLOR: #000000">0</span><span style="COLOR: #000000">]</span><span style="COLOR: #000000">=</span><span style="COLOR: #000000">0</span><span style="COLOR: #000000">;<br></span><span style="COLOR: #008080">11</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;}<br></span><span style="COLOR: #008080">12</span>&nbsp;<span style="COLOR: #000000"><br></span><span style="COLOR: #008080">13</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;String(</span><span style="COLOR: #0000ff">const</span><span style="COLOR: #000000">&nbsp;</span><span style="COLOR: #0000ff">char</span><span style="COLOR: #000000">*</span><span style="COLOR: #000000">&nbsp;s)<br></span><span style="COLOR: #008080">14</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;{<br></span><span style="COLOR: #008080">15</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;buffer</span><span style="COLOR: #000000">=</span><span style="COLOR: #0000ff">new</span><span style="COLOR: #000000">&nbsp;</span><span style="COLOR: #0000ff">char</span><span style="COLOR: #000000">[strlen(s)</span><span style="COLOR: #000000">+</span><span style="COLOR: #000000">1</span><span style="COLOR: #000000">];<br></span><span style="COLOR: #008080">16</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;strcpy(buffer,&nbsp;s);<br></span><span style="COLOR: #008080">17</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;}<br></span><span style="COLOR: #008080">18</span>&nbsp;<span style="COLOR: #000000"><br></span><span style="COLOR: #008080">19</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;String(</span><span style="COLOR: #0000ff">const</span><span style="COLOR: #000000">&nbsp;String</span><span style="COLOR: #000000">&amp;</span><span style="COLOR: #000000">&nbsp;s)<br></span><span style="COLOR: #008080">20</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;{<br></span><span style="COLOR: #008080">21</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;buffer</span><span style="COLOR: #000000">=</span><span style="COLOR: #0000ff">new</span><span style="COLOR: #000000">&nbsp;</span><span style="COLOR: #0000ff">char</span><span style="COLOR: #000000">[strlen(s.buffer)</span><span style="COLOR: #000000">+</span><span style="COLOR: #000000">1</span><span style="COLOR: #000000">];<br></span><span style="COLOR: #008080">22</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;strcpy(buffer,&nbsp;s.buffer);<br></span><span style="COLOR: #008080">23</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;}<br></span><span style="COLOR: #008080">24</span>&nbsp;<span style="COLOR: #000000"><br></span><span style="COLOR: #008080">25</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;</span><span style="COLOR: #000000">~</span><span style="COLOR: #000000">String()<br></span><span style="COLOR: #008080">26</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;{<br></span><span style="COLOR: #008080">27</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;delete[]&nbsp;buffer;<br></span><span style="COLOR: #008080">28</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;}<br></span><span style="COLOR: #008080">29</span>&nbsp;<span style="COLOR: #000000"><br></span><span style="COLOR: #008080">30</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;String</span><span style="COLOR: #000000">&amp;</span><span style="COLOR: #000000">&nbsp;</span><span style="COLOR: #0000ff">operator</span><span style="COLOR: #000000">=</span><span style="COLOR: #000000">(</span><span style="COLOR: #0000ff">const</span><span style="COLOR: #000000">&nbsp;String</span><span style="COLOR: #000000">&amp;</span><span style="COLOR: #000000">&nbsp;s)<br></span><span style="COLOR: #008080">31</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;{<br></span><span style="COLOR: #008080">32</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;delete[]&nbsp;buffer;<br></span><span style="COLOR: #008080">33</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;buffer</span><span style="COLOR: #000000">=</span><span style="COLOR: #0000ff">new</span><span style="COLOR: #000000">&nbsp;</span><span style="COLOR: #0000ff">char</span><span style="COLOR: #000000">[strlen(s.buffer)</span><span style="COLOR: #000000">+</span><span style="COLOR: #000000">1</span><span style="COLOR: #000000">];<br></span><span style="COLOR: #008080">34</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;strcpy(buffer,&nbsp;s.buffer);<br></span><span style="COLOR: #008080">35</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;}<br></span><span style="COLOR: #008080">36</span>&nbsp;<span style="COLOR: #000000">};</span></div>
<br>&nbsp;&nbsp;&nbsp; 于是我们来做一下memset。首先定义一个字符串变量，其次memset掉，让我们看看会发生什么事情：<br>
<div style="BORDER-BOTTOM: #cccccc 1px solid; BORDER-LEFT: #cccccc 1px solid; PADDING-BOTTOM: 4px; BACKGROUND-COLOR: #eeeeee; PADDING-LEFT: 4px; WIDTH: 98%; PADDING-RIGHT: 5px; FONT-SIZE: 13px; WORD-BREAK: break-all; BORDER-TOP: #cccccc 1px solid; BORDER-RIGHT: #cccccc 1px solid; PADDING-TOP: 4px"><span style="COLOR: #008080">1</span>&nbsp;<span style="COLOR: #0000ff">string</span><span style="COLOR: #000000">&nbsp;s;<br></span><span style="COLOR: #008080">2</span>&nbsp;<span style="COLOR: #000000">memset(</span><span style="COLOR: #000000">&amp;</span><span style="COLOR: #000000">s,&nbsp;</span><span style="COLOR: #000000">0</span><span style="COLOR: #000000">,&nbsp;</span><span style="COLOR: #0000ff">sizeof</span><span style="COLOR: #000000">(s));</span></div>
<br>&nbsp;&nbsp;&nbsp; 第一行我们构造了一个字符串s。这个时候字符串的构造函数就会开始运行，因此strcmp(s.buffer, "")==0。第二行我们把那个字符串给memset掉了。这个时候s.buffer==0。于是函数结束了，字符串的析构函数尝试delete这个指针。我们知道delete一个0是不会有问题的，因此程序不会发生错误。<span style="COLOR: red"><strong>我们活生生把构造函数赋值给buffer的new char[1]给丢了</strong></span>！铁定发生内存泄露！<br><br>&nbsp;&nbsp;&nbsp; 好了，提出问题总要解决问题，我们不使用memset的话，怎么初始化Student呢？这个十分好做，我们只需要为Student加上构造函数即可：<br>
<div style="BORDER-BOTTOM: #cccccc 1px solid; BORDER-LEFT: #cccccc 1px solid; PADDING-BOTTOM: 4px; BACKGROUND-COLOR: #eeeeee; PADDING-LEFT: 4px; WIDTH: 98%; PADDING-RIGHT: 5px; FONT-SIZE: 13px; WORD-BREAK: break-all; BORDER-TOP: #cccccc 1px solid; BORDER-RIGHT: #cccccc 1px solid; PADDING-TOP: 4px"><span style="COLOR: #008080">1</span>&nbsp;<span style="COLOR: #0000ff">struct</span><span style="COLOR: #000000">&nbsp;Student<br></span><span style="COLOR: #008080">2</span>&nbsp;<span style="COLOR: #000000">{<br></span><span style="COLOR: #008080">3</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;<img src="http://www.cppblog.com/Images/dot.gif">.</span><span style="COLOR: #008000">//</span><span style="COLOR: #008000">不重复那些声明</span><span style="COLOR: #008000"><br></span><span style="COLOR: #008080">4</span>&nbsp;<span style="COLOR: #008000"></span><span style="COLOR: #000000"><br></span><span style="COLOR: #008080">5</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;Student():chinese(</span><span style="COLOR: #000000">0</span><span style="COLOR: #000000">),math(</span><span style="COLOR: #000000">0</span><span style="COLOR: #000000">),english(</span><span style="COLOR: #000000">0</span><span style="COLOR: #000000">)<br></span><span style="COLOR: #008080">6</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;{<br></span><span style="COLOR: #008080">7</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;}<br></span><span style="COLOR: #008080">8</span>&nbsp;<span style="COLOR: #000000">};</span></div>
<br>&nbsp;&nbsp;&nbsp; 这样就容易多了。每当我们定义一个Student变量的时候，所有的成员都初始化好了。name和id因为string的构造函数也自己初始化了，因此所有的成员也都初始化了。加入Student用了一半我们想再初始化一下怎么办呢？也很容易：<br>
<div style="BORDER-BOTTOM: #cccccc 1px solid; BORDER-LEFT: #cccccc 1px solid; PADDING-BOTTOM: 4px; BACKGROUND-COLOR: #eeeeee; PADDING-LEFT: 4px; WIDTH: 98%; PADDING-RIGHT: 5px; FONT-SIZE: 13px; WORD-BREAK: break-all; BORDER-TOP: #cccccc 1px solid; BORDER-RIGHT: #cccccc 1px solid; PADDING-TOP: 4px"><span style="COLOR: #008080">1</span>&nbsp;<span style="COLOR: #000000">Student&nbsp;vczh;<br></span><span style="COLOR: #008080">2</span>&nbsp;<span style="COLOR: #000000"><img src="http://www.cppblog.com/Images/dot.gif">.</span><span style="COLOR: #008000">//</span><span style="COLOR: #008000">各种使用</span><span style="COLOR: #008000"><br></span><span style="COLOR: #008080">3</span>&nbsp;<span style="COLOR: #008000"></span><span style="COLOR: #000000">vczh</span><span style="COLOR: #000000">=</span><span style="COLOR: #000000">Student();</span></div>
<br>&nbsp;&nbsp;&nbsp; 经过一个等号操作符的调用，旧Student的所有成员就被一个新的初始化过的Student给覆盖了，就如同我们对一个int变量重新赋值一样常见。当然因为各种复制经常会出现，因此我们也要跟上面贴出来的string的例子一样，实现好那4个函数。至此我十分不理解为什么某些团队不允许使用构造函数，我猜就是为了可以memset，其实是很没道理的。<br><br>&nbsp;&nbsp;&nbsp; <strong>二、异常。</strong><br><br>&nbsp;&nbsp;&nbsp; 咋一看内存泄露跟异常好像没什么关系，但实际上这种情况更容易发生。我们来看一个例子：<br>
<div style="BORDER-BOTTOM: #cccccc 1px solid; BORDER-LEFT: #cccccc 1px solid; PADDING-BOTTOM: 4px; BACKGROUND-COLOR: #eeeeee; PADDING-LEFT: 4px; WIDTH: 98%; PADDING-RIGHT: 5px; FONT-SIZE: 13px; WORD-BREAK: break-all; BORDER-TOP: #cccccc 1px solid; BORDER-RIGHT: #cccccc 1px solid; PADDING-TOP: 4px"><span style="COLOR: #008080">&nbsp;1</span>&nbsp;<span style="COLOR: #0000ff">char</span><span style="COLOR: #000000">*</span><span style="COLOR: #000000">&nbsp;strA</span><span style="COLOR: #000000">=</span><span style="COLOR: #0000ff">new</span><span style="COLOR: #000000">&nbsp;</span><span style="COLOR: #0000ff">char</span><span style="COLOR: #000000">[MAX_PATH];<br></span><span style="COLOR: #008080">&nbsp;2</span>&nbsp;<span style="COLOR: #000000"></span><span style="COLOR: #0000ff">if</span><span style="COLOR: #000000">(GetXXX(strA,&nbsp;MAX_PATH)</span><span style="COLOR: #000000">==</span><span style="COLOR: #000000">ERROR)&nbsp;</span><span style="COLOR: #0000ff">goto</span><span style="COLOR: #000000">&nbsp;RELEASE_STRA;<br></span><span style="COLOR: #008080">&nbsp;3</span>&nbsp;<span style="COLOR: #000000"></span><span style="COLOR: #0000ff">char</span><span style="COLOR: #000000">*</span><span style="COLOR: #000000">&nbsp;strB</span><span style="COLOR: #000000">=</span><span style="COLOR: #0000ff">new</span><span style="COLOR: #000000">&nbsp;</span><span style="COLOR: #0000ff">char</span><span style="COLOR: #000000">[MAX_PATH];<br></span><span style="COLOR: #008080">&nbsp;4</span>&nbsp;<span style="COLOR: #000000"></span><span style="COLOR: #0000ff">if</span><span style="COLOR: #000000">(GetXXX(strB,&nbsp;MAX_PATH)</span><span style="COLOR: #000000">==</span><span style="COLOR: #000000">ERROR)&nbsp;</span><span style="COLOR: #0000ff">goto</span><span style="COLOR: #000000">&nbsp;RELEASE_STRB;<br></span><span style="COLOR: #008080">&nbsp;5</span>&nbsp;<span style="COLOR: #000000"><br></span><span style="COLOR: #008080">&nbsp;6</span>&nbsp;<span style="COLOR: #000000">DoSomething(strA,&nbsp;strB);<br></span><span style="COLOR: #008080">&nbsp;7</span>&nbsp;<span style="COLOR: #000000"><br></span><span style="COLOR: #008080">&nbsp;8</span>&nbsp;<span style="COLOR: #000000">RELEASE_STRB:<br></span><span style="COLOR: #008080">&nbsp;9</span>&nbsp;<span style="COLOR: #000000">delete[]&nbsp;strB;<br></span><span style="COLOR: #008080">10</span>&nbsp;<span style="COLOR: #000000">RELEASE_STRA:<br></span><span style="COLOR: #008080">11</span>&nbsp;<span style="COLOR: #000000">delete[]&nbsp;strA;</span></div>
<br>&nbsp;&nbsp;&nbsp; 相信这肯定是大家的常用模式。我在这里也不是教唆大家使用goto，不过对于这种例子来说，用goto是最优美的解决办法了。但是大家可以看出来，我们用的是C++，因为这里有new。如果DoSomething发生了异常怎么办呢？如果GetXXX发生了异常怎么办呢？我们这里没有任何的try-catch，一有异常，函数里克结束，两行可怜的delete就不会被执行到了，<span style="COLOR: red"><strong>于是内存泄漏发生了</strong></span>！<br><br>&nbsp;&nbsp;&nbsp; 那我们如何避免这种情况下的内存泄露呢？一些可爱的小盆友可能会想到，既然是因为没有catch异常才发生的内存泄露，那我们来catch吧：<br>
<div style="BORDER-BOTTOM: #cccccc 1px solid; BORDER-LEFT: #cccccc 1px solid; PADDING-BOTTOM: 4px; BACKGROUND-COLOR: #eeeeee; PADDING-LEFT: 4px; WIDTH: 98%; PADDING-RIGHT: 5px; FONT-SIZE: 13px; WORD-BREAK: break-all; BORDER-TOP: #cccccc 1px solid; BORDER-RIGHT: #cccccc 1px solid; PADDING-TOP: 4px"><span style="COLOR: #008080">&nbsp;1</span>&nbsp;<span style="COLOR: #0000ff">char</span><span style="COLOR: #000000">*</span><span style="COLOR: #000000">&nbsp;strA</span><span style="COLOR: #000000">=</span><span style="COLOR: #0000ff">new</span><span style="COLOR: #000000">&nbsp;</span><span style="COLOR: #0000ff">char</span><span style="COLOR: #000000">[MAX_PATH];<br></span><span style="COLOR: #008080">&nbsp;2</span>&nbsp;<span style="COLOR: #000000"></span><span style="COLOR: #0000ff">try</span><span style="COLOR: #000000"><br></span><span style="COLOR: #008080">&nbsp;3</span>&nbsp;<span style="COLOR: #000000">{<br></span><span style="COLOR: #008080">&nbsp;4</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;</span><span style="COLOR: #0000ff">if</span><span style="COLOR: #000000">(GetXXX(strA,&nbsp;MAX_PATH)</span><span style="COLOR: #000000">==</span><span style="COLOR: #000000">ERROR)&nbsp;</span><span style="COLOR: #0000ff">goto</span><span style="COLOR: #000000">&nbsp;RELEASE_STRA;<br></span><span style="COLOR: #008080">&nbsp;5</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;</span><span style="COLOR: #0000ff">char</span><span style="COLOR: #000000">*</span><span style="COLOR: #000000">&nbsp;strB</span><span style="COLOR: #000000">=</span><span style="COLOR: #0000ff">new</span><span style="COLOR: #000000">&nbsp;</span><span style="COLOR: #0000ff">char</span><span style="COLOR: #000000">[MAX_PATH];<br></span><span style="COLOR: #008080">&nbsp;6</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;</span><span style="COLOR: #0000ff">try</span><span style="COLOR: #000000"><br></span><span style="COLOR: #008080">&nbsp;7</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;{<br></span><span style="COLOR: #008080">&nbsp;8</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;</span><span style="COLOR: #0000ff">if</span><span style="COLOR: #000000">(GetXXX(strB,&nbsp;MAX_PATH)</span><span style="COLOR: #000000">==</span><span style="COLOR: #000000">ERROR)&nbsp;</span><span style="COLOR: #0000ff">goto</span><span style="COLOR: #000000">&nbsp;RELEASE_STRB;<br></span><span style="COLOR: #008080">&nbsp;9</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;DoSomething(strA,&nbsp;strB);<br></span><span style="COLOR: #008080">10</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;}<br></span><span style="COLOR: #008080">11</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;</span><span style="COLOR: #0000ff">catch</span><span style="COLOR: #000000">(<img src="http://www.cppblog.com/Images/dot.gif">)<br></span><span style="COLOR: #008080">12</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;{<br></span><span style="COLOR: #008080">13</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;delete[]&nbsp;strB;<br></span><span style="COLOR: #008080">14</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;</span><span style="COLOR: #0000ff">throw</span><span style="COLOR: #000000">;<br></span><span style="COLOR: #008080">15</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;}<br></span><span style="COLOR: #008080">16</span>&nbsp;<span style="COLOR: #000000">}<br></span><span style="COLOR: #008080">17</span>&nbsp;<span style="COLOR: #000000"></span><span style="COLOR: #0000ff">catch</span><span style="COLOR: #000000">(<img src="http://www.cppblog.com/Images/dot.gif">)<br></span><span style="COLOR: #008080">18</span>&nbsp;<span style="COLOR: #000000">{<br></span><span style="COLOR: #008080">19</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;delete[]&nbsp;strA;<br></span><span style="COLOR: #008080">20</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;</span><span style="COLOR: #0000ff">throw</span><span style="COLOR: #000000">;<br></span><span style="COLOR: #008080">21</span>&nbsp;<span style="COLOR: #000000">}<br></span><span style="COLOR: #008080">22</span>&nbsp;<span style="COLOR: #000000"><br></span><span style="COLOR: #008080">23</span>&nbsp;<span style="COLOR: #000000">RELEASE_STRB:<br></span><span style="COLOR: #008080">24</span>&nbsp;<span style="COLOR: #000000">delete[]&nbsp;strB;<br></span><span style="COLOR: #008080">25</span>&nbsp;<span style="COLOR: #000000">RELEASE_STRA:<br></span><span style="COLOR: #008080">26</span>&nbsp;<span style="COLOR: #000000">delete[]&nbsp;strA;</span></div>
<br>&nbsp;&nbsp;&nbsp; 你能接受吗？当然是不能的。问题出在哪里呢？因为C++没有try-finally。你看这些代码到处都是雷同的东西，显然我们需要编译器帮我们把这些问题搞定。最好的解决方法是什么呢？显然还是构造函数和析构函数。总之记住，<span style="COLOR: red"><strong>如果想要事情成对发生，那么使用构造函数和析构函数</strong></span>。<br><br>&nbsp;&nbsp;&nbsp; 第一步，GetXXX显然只能支持C模式的东西，因此我们要写一个支持C++的：<br>
<div style="BORDER-BOTTOM: #cccccc 1px solid; BORDER-LEFT: #cccccc 1px solid; PADDING-BOTTOM: 4px; BACKGROUND-COLOR: #eeeeee; PADDING-LEFT: 4px; WIDTH: 98%; PADDING-RIGHT: 5px; FONT-SIZE: 13px; WORD-BREAK: break-all; BORDER-TOP: #cccccc 1px solid; BORDER-RIGHT: #cccccc 1px solid; PADDING-TOP: 4px"><span style="COLOR: #008080">&nbsp;1</span>&nbsp;<span style="COLOR: #0000ff">bool</span><span style="COLOR: #000000">&nbsp;GetXXX2(</span><span style="COLOR: #0000ff">string</span><span style="COLOR: #000000">&amp;</span><span style="COLOR: #000000">&nbsp;s)<br></span><span style="COLOR: #008080">&nbsp;2</span>&nbsp;<span style="COLOR: #000000">{<br></span><span style="COLOR: #008080">&nbsp;3</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;</span><span style="COLOR: #0000ff">char</span><span style="COLOR: #000000">*</span><span style="COLOR: #000000">&nbsp;str</span><span style="COLOR: #000000">=</span><span style="COLOR: #0000ff">new</span><span style="COLOR: #000000">&nbsp;</span><span style="COLOR: #0000ff">char</span><span style="COLOR: #000000">[MAX_PATH];<br></span><span style="COLOR: #008080">&nbsp;4</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;</span><span style="COLOR: #0000ff">bool</span><span style="COLOR: #000000">&nbsp;result;<br></span><span style="COLOR: #008080">&nbsp;5</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;</span><span style="COLOR: #0000ff">try</span><span style="COLOR: #000000"><br></span><span style="COLOR: #008080">&nbsp;6</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;{<br></span><span style="COLOR: #008080">&nbsp;7</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;result</span><span style="COLOR: #000000">=</span><span style="COLOR: #000000">GetXXX(str,&nbsp;MAX_PATH);<br></span><span style="COLOR: #008080">&nbsp;8</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;</span><span style="COLOR: #0000ff">if</span><span style="COLOR: #000000">(result)s</span><span style="COLOR: #000000">=</span><span style="COLOR: #000000">str;<br></span><span style="COLOR: #008080">&nbsp;9</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;}<br></span><span style="COLOR: #008080">10</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;</span><span style="COLOR: #0000ff">catch</span><span style="COLOR: #000000">(<img src="http://www.cppblog.com/Images/dot.gif">)<br></span><span style="COLOR: #008080">11</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;{<br></span><span style="COLOR: #008080">12</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;delete[]&nbsp;str;<br></span><span style="COLOR: #008080">13</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;</span><span style="COLOR: #0000ff">throw</span><span style="COLOR: #000000">;<br></span><span style="COLOR: #008080">14</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;}<br></span><span style="COLOR: #008080">15</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;delete[]&nbsp;str;<br></span><span style="COLOR: #008080">16</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;</span><span style="COLOR: #0000ff">return</span><span style="COLOR: #000000">&nbsp;result;<br></span><span style="COLOR: #008080">17</span>&nbsp;<span style="COLOR: #000000">}</span></div>
<br>&nbsp;&nbsp;&nbsp; 借助这个函数我们可以看到，因为有了GetXXX这种C的东西，导致我们多了多少麻烦。不过这总是一劳永逸的，有了GetXXX2和修改之后的DoSomething2之后，我们就可以用更简单的方法来做了：<br>
<div style="BORDER-BOTTOM: #cccccc 1px solid; BORDER-LEFT: #cccccc 1px solid; PADDING-BOTTOM: 4px; BACKGROUND-COLOR: #eeeeee; PADDING-LEFT: 4px; WIDTH: 98%; PADDING-RIGHT: 5px; FONT-SIZE: 13px; WORD-BREAK: break-all; BORDER-TOP: #cccccc 1px solid; BORDER-RIGHT: #cccccc 1px solid; PADDING-TOP: 4px"><span style="COLOR: #008080">1</span>&nbsp;<span style="COLOR: #0000ff">string</span><span style="COLOR: #000000">&nbsp;a,b;<br></span><span style="COLOR: #008080">2</span>&nbsp;<span style="COLOR: #000000"></span><span style="COLOR: #0000ff">if</span><span style="COLOR: #000000">(GetXXX2(a)&nbsp;</span><span style="COLOR: #000000">&amp;&amp;</span><span style="COLOR: #000000">&nbsp;GetXXX2(b))<br></span><span style="COLOR: #008080">3</span>&nbsp;<span style="COLOR: #000000">{<br></span><span style="COLOR: #008080">4</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;DoSomething2(a,&nbsp;b);<br></span><span style="COLOR: #008080">5</span>&nbsp;<span style="COLOR: #000000">}</span></div>
<br>&nbsp;&nbsp;&nbsp; 多么简单易懂。这个代码在任何地方发生了异常，所有new的东西都会被delete。这就是析构函数的一个好处。一个变量的析构函数在这个变量超出了作用域的时候一定会被调用，无论代码是怎么走出去的。<br><br>&nbsp;&nbsp;&nbsp; 今天就说到这里了。说了这么多还是想让大家不要小看构造函数和析构函数。那种微不足道的因为一小部分不是瓶颈的性能问题而放弃构造函数和析构函数的做法，终究是要为了修bug而加班的。只要明白并用好了构造函数、析构函数和异常，那么C++的特性也可以跟C一样清楚明白便于理解，而且写出来的代码更好看的。大家期待第三篇哈。 
<img src ="http://www.cppblog.com/vczh/aggbug/118603.html" width = "1" height = "1" /><br><br><div align=right><a style="text-decoration:none;" href="http://www.cppblog.com/vczh/" target="_blank">陈梓瀚(vczh)</a> 2010-06-24 02:12 <a href="http://www.cppblog.com/vczh/archive/2010/06/24/118603.html#Feedback" target="_blank" style="text-decoration:none;">发表评论</a></div>]]></description></item><item><title>C++实用技巧（一）</title><link>http://www.cppblog.com/vczh/archive/2010/06/22/118493.html</link><dc:creator>陈梓瀚(vczh)</dc:creator><author>陈梓瀚(vczh)</author><pubDate>Tue, 22 Jun 2010 13:16:00 GMT</pubDate><guid>http://www.cppblog.com/vczh/archive/2010/06/22/118493.html</guid><wfw:comment>http://www.cppblog.com/vczh/comments/118493.html</wfw:comment><comments>http://www.cppblog.com/vczh/archive/2010/06/22/118493.html#Feedback</comments><slash:comments>29</slash:comments><wfw:commentRss>http://www.cppblog.com/vczh/comments/commentRss/118493.html</wfw:commentRss><trackback:ping>http://www.cppblog.com/vczh/services/trackbacks/118493.html</trackback:ping><description><![CDATA[&nbsp;&nbsp;&nbsp; 复杂的东西写多了，如今写点简单的好了。由于功能上的需要，<a style="TEXT-DECORATION: underline" href="http://vlpp.codeplex.com/" target=_blank>Vczh Library++3.0</a>被我搞得很离谱。为了开发维护的遍历、减少粗心犯下的错误以及增强单元测试、回归测试和测试工具，因此记录下一些开发上的小技巧，以便抛砖引玉，造福他人。欢迎高手来喷，菜鸟膜拜。<br><br>&nbsp;&nbsp;&nbsp; C++实谓各种语言中的软肋，功能强大，陷阱更强大。当然我认为一门语言用得不好完全是程序员的责任，不过因为C++涉及到的概念实在是太多，想用好实在也不是一件容易的事情。C++开发的时候总是会遇到各种各样的问题，其中最严重的无非是内存相关的。C语言由于结构简单，内存处理起来虽然不得力，但总的来说惯用法已经深入人心，因此也不会造成什么很难发现的错误。C++就不一样了。有了虚函数、构造函数、析构函数、复制构造函数和operator=重载之后，还是有很多人喜欢把一个类直接写进文件流，或者拿来memset，代码一团乱麻，不知悔改也。但是不能因此因噎废食，就像某人因为C++带来的心智问题太多，自己搞不定，自己团队也搞不定，就说C++不好一样。<br><br>&nbsp;&nbsp;&nbsp; 因此第一篇文章主要针对内存来讲。我们处理内存，第一件事就是不要有内存泄露。内存泄露不能等到测试的时候，通过长时间运行程序并观察任务管理器的方法来做，这显然已经晚了。幸好Visual C++给了我们一个十分好用的工具：_CrtDumpMemoryLeaks函数。这个函数会在Debug模式下往Visual Studio的output窗口打印出那个时候你new（malloc）了但是还没delete（free）的所有内存块的地址、长度、前N个字节的内容和其他信息。怎么做呢？其实很简单：<br>
<div style="BORDER-BOTTOM: #cccccc 1px solid; BORDER-LEFT: #cccccc 1px solid; PADDING-BOTTOM: 4px; BACKGROUND-COLOR: #eeeeee; PADDING-LEFT: 4px; WIDTH: 98%; PADDING-RIGHT: 5px; FONT-SIZE: 13px; WORD-BREAK: break-all; BORDER-TOP: #cccccc 1px solid; BORDER-RIGHT: #cccccc 1px solid; PADDING-TOP: 4px"><span style="COLOR: #008080">&nbsp;1</span>&nbsp;<span style="COLOR: #0000ff">#define</span><span style="COLOR: #000000">&nbsp;_CRTDBG_MAP_ALLOC</span><span style="COLOR: #000000"><br></span><span style="COLOR: #008080">&nbsp;2</span>&nbsp;<span style="COLOR: #000000">#include&nbsp;</span><span style="COLOR: #000000">&lt;</span><span style="COLOR: #000000">stdlib.h</span><span style="COLOR: #000000">&gt;</span><span style="COLOR: #000000"><br></span><span style="COLOR: #008080">&nbsp;3</span>&nbsp;<span style="COLOR: #000000">#include&nbsp;</span><span style="COLOR: #000000">&lt;</span><span style="COLOR: #000000">crtdbg.h</span><span style="COLOR: #000000">&gt;</span><span style="COLOR: #000000"><br></span><span style="COLOR: #008080">&nbsp;4</span>&nbsp;<span style="COLOR: #000000">#include&nbsp;</span><span style="COLOR: #000000">&lt;</span><span style="COLOR: #000000">windows.h</span><span style="COLOR: #000000">&gt;</span><span style="COLOR: #000000"><br></span><span style="COLOR: #008080">&nbsp;5</span>&nbsp;<span style="COLOR: #000000"><br></span><span style="COLOR: #008080">&nbsp;6</span>&nbsp;<span style="COLOR: #000000"></span><span style="COLOR: #0000ff">int</span><span style="COLOR: #000000">&nbsp;wmain(vint&nbsp;argc&nbsp;,&nbsp;wchar_t</span><span style="COLOR: #000000">*</span><span style="COLOR: #000000">&nbsp;args[])<br></span><span style="COLOR: #008080">&nbsp;7</span>&nbsp;<span style="COLOR: #000000">{<br></span><span style="COLOR: #008080">&nbsp;8</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;</span><span style="COLOR: #008000">//</span><span style="COLOR: #008000">&nbsp;这里运行程序，并在下面的函数调用之前delete掉所有new的东西</span><span style="COLOR: #008000"><br></span><span style="COLOR: #008080">&nbsp;9</span>&nbsp;<span style="COLOR: #008000"></span><span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;_CrtDumpMemoryLeaks();<br></span><span style="COLOR: #008080">10</span>&nbsp;<span style="COLOR: #000000">&nbsp;&nbsp;&nbsp;&nbsp;</span><span style="COLOR: #0000ff">return</span><span style="COLOR: #000000">&nbsp;</span><span style="COLOR: #000000">0</span><span style="COLOR: #000000">;<br></span><span style="COLOR: #008080">11</span>&nbsp;<span style="COLOR: #000000">}</span></div>
<br>&nbsp;&nbsp;&nbsp; 我们只需要在注释的地方完成我们程序的功能，然后确信自己已经delete掉所有应该delete的东西，最后_CrtDumpMemoryLeaks()函数调用的时候就可以打印出没被delete的东西了。这个方法十分神奇，因为你只需要在main函数所在的cpp文件这么#include一下，所有的cpp文件里面的new都会受到监视，跟平常所用的用宏把new给换掉的这种破方法截然不同。如果你使用了全局变量的话也要小心，因为全局变量的析构函数是在main函数结束之后才执行的，因此如果在全局变量的析构函数里面delete的东西仍然会被_CrtDumpMemoryLeaks函数当成泄露掉的资源对待。当然本人认为全局变量可以用，但是全局变量的赋值必须在main里面做，释放也是，除非那个全局变量的构造函数没有申请任何内存，所以这也是一个很好的检查方法。<br><br>&nbsp;&nbsp;&nbsp; 不过上面也仅仅是一个告诉你有没有内存泄漏的方法罢了。那么如何避免内存泄露呢？当然在设计一些性能要求没有比操作系统更加严格的程序的时候，可以使用以下方法：<br>&nbsp;&nbsp;&nbsp; 1、如果构造函数new了一个对象<span style="COLOR: red"><strong>并使用成员指针变量</strong></span>保存的话，那么必须在析构函数delete它，并且不能有为了某些便利而将这个对象的所有权转让出去的事情发生。<br>&nbsp;&nbsp;&nbsp; 2、在能使用shared_ptr的时候，尽量使用shared_ptr。shared_ptr只要你不发生循环引用，那么这个东西可以安全地互相传递、随便你放在什么容器里面添加删除、你想放哪里就放在哪里，再也不用考虑这个对象的生命周期问题了。<br>&nbsp;&nbsp;&nbsp; 3、不要在有构造函数和析构函数的对象上使用memset（或者memcpy）。如果一个对象需要memset，那么在该对象的构造函数里面memset自己。如果你需要memset一个对象数组，那也在该对象的构造函数里面memset自己。<span style="COLOR: red"><strong>如果你需要memset一个没有构造函数的复杂对象，那么请为他添加一个构造函数，除非那是别人的API提供的东西</strong></span>。<br>&nbsp;&nbsp;&nbsp; 4、如果一个对象是继承了其他东西，或者某些成员被标记了virtual的话，绝对不要memset。对象是独立的，也就是说父类内部结构的演变不需要对子类负责。哪天父类里面加了一个string成员，被子类一memset，就欲哭无泪了。<br>&nbsp;&nbsp;&nbsp; 5、如果需要为一个对象定义构造函数，那么连复制构造函数、operator=重载和析构函数都全部写全。如果不想写复制构造函数和operator=的话，那么用一个空的实现写在private里面，确保任何试图调用这些函数的代码都出现编译错误。<br>&nbsp;&nbsp;&nbsp; 6、如果你实在很喜欢C语言的话，那麻烦换一个只支持C不支持C++的编译器，全面杜绝因为误用了C++而导致你的C坏掉的情况出现。<br><br>&nbsp;&nbsp;&nbsp; 什么是循环引用呢？如果两个对象互相使用一个shared_ptr成员变量直接或者间接指向对方的话，就是循环引用了。在这种情况下引用计数会失效，因为就算外边的shared_ptr全释放光了，引用计数也不会是0的。<br><br>&nbsp;&nbsp;&nbsp; 今天就说到这里了，过几天我高兴的话再写一篇续集，如果我持续高兴的话呢&#8230;&#8230;嗯嗯&#8230;&#8230;。 
<img src ="http://www.cppblog.com/vczh/aggbug/118493.html" width = "1" height = "1" /><br><br><div align=right><a style="text-decoration:none;" href="http://www.cppblog.com/vczh/" target="_blank">陈梓瀚(vczh)</a> 2010-06-22 21:16 <a href="http://www.cppblog.com/vczh/archive/2010/06/22/118493.html#Feedback" target="_blank" style="text-decoration:none;">发表评论</a></div>]]></description></item></channel></rss>