C++博客-rdu-cpp-随笔分类-论坛拾珠

dangerous c-styled func: gets

rdu — Wed, 21 Jan 2009 07:37:00 GMT

如果您使用cin來取得使用者的輸入字串，則您會發現輸入字串時中間不能包括空白，如果您想要在輸入字串時包括空白，您必須使用gets()函式，例如：

char str[80];
cout << "輸入字串：";
gets(str);
cout << "輸入的字串：" << str << endl;

使用gets()函式時有一點必須注意，就是它並不會檢查使用者的輸入是否超出字元陣列的長度，使用時必須小心，有的編譯器會提示警告訊息。

: the `gets' function is dangerous and should not be used.

对于代码：

1int main()
2{
3    char str[9];
4    puts("input a string:");
5    gets(str);
6    puts(str);
7    return 0;
8}

在VS 2005中，如果输入了一个长度大于8（9-1）的字符串，VS 2005在编译期不给出上述警告，但是在执行完毕后会跳出对话框提示：
Run-Time Check Failure #2 - Stack around the variable 'str' was corrupted.

rdu 2009-01-21 15:37 发表评论

ungetc的用法

rdu — Tue, 20 Jan 2009 13:54:00 GMT

C/C++ code

ungetc　　函数名: ungetc
　　功 能: 把一个字符退回到输入流中
　　用 法: int ungetc(char c, FILE *stream);
　　输入参数：c 要写入的字符，stream 文件流指针
　　输出参数：字符c - 操作成功，EOF - 操作失败
　　程序例:
　　#include 
   using namespace std;
　　int main( void )
　　{
　　int i=0;
　　char ch;
　　puts("Input an integer followed by a char:");
　　/* read chars until non digit or EOF */
　　while((ch = getchar()) != EOF && isdigit(ch))
　　i = 10 * i + ch - 48; /* convert ASCII into int value */
　　/* if non digit char was read, push it back into input buffer */
　　if (ch != EOF)
　　ungetc(ch, stdin);
　　printf("i = %d, next char in buffer = %c\n", i, getchar());
　　return 0;
　　}

rdu 2009-01-20 21:54 发表评论

位拷贝和值拷贝

rdu — Tue, 20 Jan 2009 13:05:00 GMT

加为好友

发送私信

在线聊天

chenxiong115
青雄雄
等级:
可用分等级：短工
总技术分：10
总技术分排名：223923

发表于：2008-11-07 18:54:4454楼得分:0

两个对象经过位拷贝之后，除了这两个对象的地址不同以为，它们成员变量的值绝对相同。

要用值拷贝就是说要你在有指针成员变量的时候一定要写拷贝构造函数和重载=。

写程序注意就行。

ASSERT(位拷贝==浅拷贝);
ASSERT(值拷贝==深拷贝);

加为好友

发送私信

在线聊天

jinder22
像玫瑰花和亚里士多德一样美丽
等级:
可用分等级：富农
总技术分：27
总技术分排名：167798

发表于：2008-11-21 16:34:1789楼得分:0

#include
#include
using namespace std;
class CBase
{
public:
int *p;
CBase(){}
~CBase()
{
cout < <"释放堆地址" <

delete p;

}
CBase(const CBase &cbase)
{
p=cbase.p;//这样跟默认的位拷贝没有区别
//p=new int;
//*p = *(cbase.p); // 这样才是深拷贝！！
}
CBase(int *p)
{
this->p = p;
}

CBase &operator=(const CBase &cbase)//赋值函数
{
p=cbase.p;
}

void print()
{
cout < <"对象" < }
};
int main()
{
//int a=8;
//CBase p(&a);//错误,最后p指向了栈内存了
int *a = new int(8);
int *b = new int(4);
int i =1;
int j =2;
int *ii,*pp;
*ii=2,*pp=4;
cout < < *ii < < " " < < ii < < endl;
cout < < *pp < < " " < < pp < < endl;
//pp=NULL;
//pp=ii;
*pp=*ii;
cout < < *ii < < " " < < ii < < endl;
cout < < *pp < < " " < < pp < < endl;

cout < < i < < &i;

CBase p(a);
p.print();
CBase p1(p);
p1.print();
CBase p2(b);
p2=p;
p2.print();

return 0;
}

rdu 2009-01-20 21:05 发表评论

Console Closing Down

rdu — Tue, 20 Jan 2009 09:19:00 GMT

Zolaboony (1)	May 19, 2008 at 5:30am
Hi, i am new to C++ and have just written my "Hello World" program. It worked all right but the console/cmd closes down instantly. If you tell me why it is closing down it would be very helpful.

Duoas (1617) May 19, 2008 at 5:40am

It is because your IDE is too stupid to know that a console application run from the IDE should have an automatic pause at the end.

Add the following to the end of your main() function to fix it:

1 2 3 4 5 6 7

  ...
                        std::cout << "Press ENTER to continue...";
                        std::cin.ignore( std::numeric_limits::max(), '\n' );
                        return 0;
                        }

You'll need to #include

Enjoy.

ropez (312) May 25, 2008 at 1:44pm

First I would search for the setting in my IDE that says "Keep console window open after program terminates".

If I didn't find it, I'd send a request for it to be included in the next version.

In the meantime: All the suggestions so far assumes that the program reach the end of main. Neither of you considered exceptions, or something like this in main:

1 2

if (somethingFailed())
                        return SOME_ERROR_CODE;

I suggest creating this small tool:

1 2 3 4 5 6 7 8

class KeepRunning {
                        public:
                        ~KeepRunning() {
                        // Whatever code you prefer to keep the program running, e.g.
                        system("pause"); // "Press enter"
                        sleep(5); // Wait 5 seconds
                        }
                        };

In your main function:

1 2 3 4 5 6

int main() {
                        KeepRunning kr;
                        // code
                        } // Program stops here

This way the program must keep the console open, even if it doesn't reach the end of main.

BTW: Of course, remember to remove this code before the program is "released".

rdu 2009-01-20 17:19 发表评论