对有关数据类型转换的整理

int i = 100;
long l = 2001;
float f=300.2;
double d=12345.119;
char username[]="程佩君";
char temp[200];
char *buf;
CString str;
_variant_t v1;
_bstr_t v2;

一、其它数据类型转换为字符串

  • 短整型(int)
    itoa(i,temp,10);///将i转换为字符串放入temp中,最后一个数字表示十进制
    itoa(i,temp,2); ///按二进制方式转换
  • 长整型(long)
    ltoa(l,temp,10);
  • 浮点数(float,double)
    用fcvt可以完成转换,这是MSDN中的例子:
    int decimal, sign;
    char *buffer;
    double source = 3.1415926535;
    buffer = _fcvt( source, 7, &decimal, &sign );
    运行结果:source: 3.1415926535 buffer: '31415927' decimal: 1 sign: 0
    decimal表示小数点的位置,sign表示符号:0为正数,1为负数
  • CString变量
    str = "2008北京奥运";
    buf = (LPSTR)(LPCTSTR)str;
  • BSTR变量
    BSTR bstrValue = ::SysAllocString(L"程序员");
    char * buf = _com_util::ConvertBSTRToString(bstrValue);
    SysFreeString(bstrValue);
    AfxMessageBox(buf);
    delete(buf);
  • CComBSTR变量
    CComBSTR bstrVar("test");
    char *buf = _com_util::ConvertBSTRToString(bstrVar.m_str);
    AfxMessageBox(buf);
    delete(buf);
  • _bstr_t变量
    _bstr_t类型是对BSTR的封装,因为已经重载了=操作符,所以很容易使用
    _bstr_t bstrVar("test");
    const char *buf = bstrVar;///不要修改buf中的内容
    AfxMessageBox(buf);

  • 通用方法(针对非COM数据类型)
    用sprintf完成转换
    char buffer[200]; char c = '1'; int i = 35; long j = 1000; float f = 1.7320534f; sprintf( buffer, "%c",c); sprintf( buffer, "%d",i); sprintf( buffer, "%d",j); sprintf( buffer, "%f",f); 

二、字符串转换为其它数据类型
strcpy(temp,"123");

  • 短整型(int)
    i = atoi(temp);
  • 长整型(long)
    l = atol(temp);
  • 浮点(double)
    d = atof(temp);
  • CString变量
    CString name = temp;
  • BSTR变量
    BSTR bstrValue = ::SysAllocString(L"程序员");
    ...///完成对bstrValue的使用
    SysFreeString(bstrValue);
  • CComBSTR变量
    CComBSTR类型变量可以直接赋值
    CComBSTR bstrVar1("test");
    CComBSTR bstrVar2(temp);
  • _bstr_t变量
    _bstr_t类型的变量可以直接赋值
    _bstr_t bstrVar1("test");
    _bstr_t bstrVar2(temp);

三、其它数据类型转换到CString
使用CString的成员函数Format来转换,例如:

  • 整数(int)
    str.Format("%d",i);
  • 浮点数(float)
    str.Format("%f",i);
  • 字符串指针(char *)等已经被CString构造函数支持的数据类型可以直接赋值
    str = username;
  • 对于Format所不支持的数据类型,可以通过上面所说的关于其它数据类型转化到char *的方法先转到char *,然后赋值给CString变量。

四、BSTR、_bstr_t与CComBSTR

  • CComBSTR 是ATL对BSTR的封装,_bstr_t是C++对BSTR的封装,BSTR是32位指针,但并不直接指向字串的缓冲区。
    char *转换到BSTR可以这样:
    BSTR b=_com_util::ConvertStringToBSTR("数据");///使用前需要加上comutil.h和comsupp.lib
    SysFreeString(bstrValue);
    反之可以使用
    char *p=_com_util::ConvertBSTRToString(b);
    delete p;
    具体可以参考一,二段落里的具体说明。

    CComBSTR与_bstr_t对大量的操作符进行了重载,可以直接进行=,!=,==等操作,所以使用非常方便。
    特别是_bstr_t,建议大家使用它。

五、VARIANT 、_variant_t 与 COleVariant

  • VARIANT的结构可以参考头文件VC98\Include\OAIDL.H中关于结构体tagVARIANT的定义。
    对于VARIANT变量的赋值:首先给vt成员赋值,指明数据类型,再对联合结构中相同数据类型的变量赋值,举个例子:
    VARIANT va;
    int a=2001;
    va.vt=VT_I4;///指明整型数据
    va.lVal=a; ///赋值
  • _variant_t是VARIANT的封装类,其赋值可以使用强制类型转换,其构造函数会自动处理这些数据类型。
    使用时需加上#include <comdef.h>
    例如:
    long l=222;
    ing i=100;
    _variant_t lVal(l);
    lVal = (long)i;

  • COleVariant的使用与_variant_t的方法基本一样,请参考如下例子:
    COleVariant v3 = "字符串", v4 = (long)1999;
    CString str =(BSTR)v3.pbstrVal;
    long i = v4.lVal;

    //////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
  • 本主题演示如何将各种 C++ 字符串类型转换为其他字符串。可以转换的字符串类型包括 char *wchar_t*_bstr_tCComBSTRCStringbasic_stringSystem.String。在所有情况下,在将字符串转换为新类型时,都会创建字符串的副本。对新字符串进行的任何更改都不会影响原始字符串,反之亦然。

    从 char * 转换

    示例

    说明

    此示例演示如何从 char * 转换为上面列出的其他字符串类型。

    // convert_from_char.cpp
    // compile with /clr /link comsuppw.lib
    
    #include <iostream>
    #include <stdlib.h>
    #include <string>
    
    #include "atlbase.h"
    #include "atlstr.h"
    #include "comutil.h"
    
    using namespace std;
    using namespace System;
    
    int main()
    {
        char *orig = "Hello, World!";
        cout << orig << " (char *)" << endl;
    
        // Convert to a wchar_t*
        size_t origsize = strlen(orig) + 1;
        const size_t newsize = 100;
        size_t convertedChars = 0;
        wchar_t wcstring[newsize];
        mbstowcs_s(&convertedChars, wcstring, origsize, orig, _TRUNCATE);
        wcscat_s(wcstring, L" (wchar_t *)");
        wcout << wcstring << endl;
    
        // Convert to a _bstr_t
        _bstr_t bstrt(orig);
        bstrt += " (_bstr_t)";
        cout << bstrt << endl;
    
        // Convert to a CComBSTR
        CComBSTR ccombstr(orig);
        if (ccombstr.Append(L" (CComBSTR)") == S_OK)
        {
            CW2A printstr(ccombstr);
            cout << printstr << endl;
        }
    
        // Convert to a CString
        CString cstring(orig);
        cstring += " (CString)";
        cout << cstring << endl;
    
        // Convert to a basic_string
        string basicstring(orig);
        basicstring += " (basic_string)";
        cout << basicstring << endl;
    
        // Convert to a System::String
        String ^systemstring = gcnew String(orig);
        systemstring += " (System::String)";
        Console::WriteLine("{0}", systemstring);
        delete systemstring;
    }

    输出

    Hello, World! (char *)
    Hello, World! (wchar_t *)
    Hello, World! (_bstr_t)
    Hello, World! (CComBSTR)
    Hello, World! (CString)
    Hello, World! (basic_string)
    Hello, World! (System::String)

    从 wchar_t * 转换

    示例

    说明

    此示例演示如何从 wchar_t * 转换为上面列出的其他字符串类型。

    // convert_from_wchar_t.cpp
    // compile with /clr /link comsuppw.lib
    
    #include <iostream>
    #include <stdlib.h>
    #include <string>
    
    #include "atlbase.h"
    #include "atlstr.h"
    #include "comutil.h"
    
    using namespace std;
    using namespace System;
    
    int main()
    {
        wchar_t *orig = L"Hello, World!";
        wcout << orig << L" (wchar_t *)" << endl;
    
        // Convert to a char*
        size_t origsize = wcslen(orig) + 1;
        const size_t newsize = 100;
        size_t convertedChars = 0;
        char nstring[newsize];
        wcstombs_s(&convertedChars, nstring, origsize, orig, _TRUNCATE);
        strcat_s(nstring, " (char *)");
        cout << nstring << endl;
    
        // Convert to a _bstr_t
        _bstr_t bstrt(orig);
        bstrt += " (_bstr_t)";
        cout << bstrt << endl;
    
        // Convert to a CComBSTR
        CComBSTR ccombstr(orig);
        if (ccombstr.Append(L" (CComBSTR)") == S_OK)
        {
            CW2A printstr(ccombstr);
            cout << printstr << endl;
        }
    
        // Convert to a CString
        CString cstring(orig);
        cstring += " (CString)";
        cout << cstring << endl;
    
        // Convert to a basic_string
        wstring basicstring(orig);
        basicstring += L" (basic_string)";
        wcout << basicstring << endl;
    
        // Convert to a System::String
        String ^systemstring = gcnew String(orig);
        systemstring += " (System::String)";
        Console::WriteLine("{0}", systemstring);
        delete systemstring;
    }

    输出

    Hello, World! (wchar_t *)
    Hello, World! (char *)
    Hello, World! (_bstr_t)
    Hello, World! (CComBSTR)
    Hello, World! (CString)
    Hello, World! (basic_string)
    Hello, World! (System::String)

    从 _bstr_t 转换

    示例

    说明

    此示例演示如何从 _bstr_t 转换为上面列出的其他字符串类型。

    // convert_from_bstr_t.cpp
    // compile with /clr /link comsuppw.lib
    
    #include <iostream>
    #include <stdlib.h>
    #include <string>
    
    #include "atlbase.h"
    #include "atlstr.h"
    #include "comutil.h"
    
    using namespace std;
    using namespace System;
    
    int main()
    {
        _bstr_t orig("Hello, World!");
        wcout << orig << " (_bstr_t)" << endl;
    
        // Convert to a char*
        const size_t newsize = 100;
        char nstring[newsize];
        strcpy_s(nstring, (char *)orig);
        strcat_s(nstring, " (char *)");
        cout << nstring << endl;
    
        // Convert to a wchar_t*
        wchar_t wcstring[newsize];
        wcscpy_s(wcstring, (wchar_t *)orig);
        wcscat_s(wcstring, L" (wchar_t *)");
        wcout << wcstring << endl;
    
        // Convert to a CComBSTR
        CComBSTR ccombstr((char *)orig);
        if (ccombstr.Append(L" (CComBSTR)") == S_OK)
        {
            CW2A printstr(ccombstr);
            cout << printstr << endl;
        }
    
        // Convert to a CString
        CString cstring((char *)orig);
        cstring += " (CString)";
        cout << cstring << endl;
    
        // Convert to a basic_string
        string basicstring((char *)orig);
        basicstring += " (basic_string)";
        cout << basicstring << endl;
    
        // Convert to a System::String
        String ^systemstring = gcnew String((char *)orig);
        systemstring += " (System::String)";
        Console::WriteLine("{0}", systemstring);
        delete systemstring;
    }

    输出

    Hello, World! (_bstr_t)
    Hello, World! (char *)
    Hello, World! (wchar_t *)
    Hello, World! (CComBSTR)
    Hello, World! (CString)
    Hello, World! (basic_string)
    Hello, World! (System::String)

    从 CComBSTR 转换

    示例

    说明

    此示例演示如何从 CComBSTR 转换为上面列出的其他字符串类型。

    // convert_from_ccombstr.cpp
    // compile with /clr /link comsuppw.lib
    
    #include <iostream>
    #include <stdlib.h>
    #include <string>
    
    #include "atlbase.h"
    #include "atlstr.h"
    #include "comutil.h"
    #include "vcclr.h"
    
    using namespace std;
    using namespace System;
    using namespace System::Runtime::InteropServices;
    
    int main()
    {
        CComBSTR orig("Hello, World!");
        CW2A printstr(orig);
        cout << printstr << " (CComBSTR)" << endl;
    
        // Convert to a char*
        const size_t newsize = 100;
        char nstring[newsize];
        CW2A tmpstr1(orig);
        strcpy_s(nstring, tmpstr1);
        strcat_s(nstring, " (char *)");
        cout << nstring << endl;
    
        // Convert to a wchar_t*
        wchar_t wcstring[newsize];
        wcscpy_s(wcstring, orig);
        wcscat_s(wcstring, L" (wchar_t *)");
        wcout << wcstring << endl;
    
        // Convert to a _bstr_t
        _bstr_t bstrt(orig);
        bstrt += " (_bstr_t)";
        cout << bstrt << endl;
    
        // Convert to a CString
        CString cstring(orig);
        cstring += " (CString)";
        cout << cstring << endl;
    
        // Convert to a basic_string
        wstring basicstring(orig);
        basicstring += L" (basic_string)";
        wcout << basicstring << endl;
    
        // Convert to a System::String
        String ^systemstring = gcnew String(orig);
        systemstring += " (System::String)";
        Console::WriteLine("{0}", systemstring);
        delete systemstring;
    }

    输出

    Hello, World! (CComBSTR)
    Hello, World! (char *)
    Hello, World! (wchar_t *)
    Hello, World! (_bstr_t)
    Hello, World! (CString)
    Hello, World! (basic_string)
    Hello, World! (System::String)

    从 CString 转换

    示例

    说明

    此示例演示如何从 CString 转换为上面列出的其他字符串类型。

    // convert_from_cstring.cpp
    // compile with /clr /link comsuppw.lib
    
    #include <iostream>
    #include <stdlib.h>
    #include <string>
    
    #include "atlbase.h"
    #include "atlstr.h"
    #include "comutil.h"
    
    using namespace std;
    using namespace System;
    
    int main()
    {
        CString orig("Hello, World!");
        wcout << orig << " (CString)" << endl;
    
        // Convert to a char*
        const size_t newsize = 100;
        char nstring[newsize];
        strcpy_s(nstring, orig);
        strcat_s(nstring, " (char *)");
        cout << nstring << endl;
    
        // Convert to a wchar_t*
        // You must first convert to a char * for this to work.
        size_t origsize = strlen(orig) + 1;
        size_t convertedChars = 0;
        wchar_t wcstring[newsize];
        mbstowcs_s(&convertedChars, wcstring, origsize, orig, _TRUNCATE);
        wcscat_s(wcstring, L" (wchar_t *)");
        wcout << wcstring << endl;
    
        // Convert to a _bstr_t
        _bstr_t bstrt(orig);
        bstrt += " (_bstr_t)";
        cout << bstrt << endl;
    
        // Convert to a CComBSTR
        CComBSTR ccombstr(orig);
        if (ccombstr.Append(L" (CComBSTR)") == S_OK)
        {
            CW2A printstr(ccombstr);
            cout << printstr << endl;
        }
    
        // Convert to a basic_string
        string basicstring(orig);
        basicstring += " (basic_string)";
        cout << basicstring << endl;
    
        // Convert to a System::String
        String ^systemstring = gcnew String(orig);
        systemstring += " (System::String)";
        Console::WriteLine("{0}", systemstring);
        delete systemstring;
    }

    输出

    Hello, World! (CString)
    Hello, World! (char *)
    Hello, World! (wchar_t *)
    Hello, World! (_bstr_t)
    Hello, World! (CComBSTR)
    Hello, World! (basic_string)
    Hello, World! (System::String)

    从 basic_string 转换

    示例

    说明

    此示例演示如何从 basic_string 转换为上面列出的其他字符串类型。

    // convert_from_basic_string.cpp
    // compile with /clr /link comsuppw.lib
    
    #include <iostream>
    #include <stdlib.h>
    #include <string>
    
    #include "atlbase.h"
    #include "atlstr.h"
    #include "comutil.h"
    
    using namespace std;
    using namespace System;
    
    int main()
    {
        string orig("Hello, World!");
        cout << orig << " (basic_string)" << endl;
    
        // Convert to a char*
        const size_t newsize = 100;
        char nstring[newsize];
        strcpy_s(nstring, orig.c_str());
        strcat_s(nstring, " (char *)");
        cout << nstring << endl;
    
        // Convert to a wchar_t*
        // You must first convert to a char * for this to work.
        size_t origsize = strlen(orig.c_str()) + 1;
        size_t convertedChars = 0;
        wchar_t wcstring[newsize];
        mbstowcs_s(&convertedChars, wcstring, origsize, orig.c_str(), _TRUNCATE);
        wcscat_s(wcstring, L" (wchar_t *)");
        wcout << wcstring << endl;
    
        // Convert to a _bstr_t
        _bstr_t bstrt(orig.c_str());
        bstrt += " (_bstr_t)";
        cout << bstrt << endl;
    
        // Convert to a CComBSTR
        CComBSTR ccombstr(orig.c_str());
        if (ccombstr.Append(L" (CComBSTR)") == S_OK)
        {
            CW2A printstr(ccombstr);
            cout << printstr << endl;
        }
    
        // Convert to a CString
        CString cstring(orig.c_str());
        cstring += " (CString)";
        cout << cstring << endl;
    
        // Convert to a System::String
        String ^systemstring = gcnew String(orig.c_str());
        systemstring += " (System::String)";
        Console::WriteLine("{0}", systemstring);
        delete systemstring;
    }

    输出

    Hello, World! (basic_string)
    Hello, World! (char *)
    Hello, World! (wchar_t *)
    Hello, World! (_bstr_t)
    Hello, World! (CComBSTR)
    Hello, World! (CString)
    Hello, World! (System::String)

    从 System::String 转换

    示例

    说明

    此示例演示如何从 System.String 转换为上面列出的其他字符串类型。

    // convert_from_system_string.cpp
    // compile with /clr /link comsuppw.lib
    
    #include <iostream>
    #include <stdlib.h>
    #include <string>
    
    #include "atlbase.h"
    #include "atlstr.h"
    #include "comutil.h"
    #include "vcclr.h"
    
    using namespace std;
    using namespace System;
    using namespace System::Runtime::InteropServices;
    
    int main()
    {
        String ^orig = gcnew String("Hello, World!");
        Console::WriteLine("{0} (System::String)", orig);
    
        pin_ptr<const wchar_t> wch = PtrToStringChars(orig);
    
        // Convert to a char*
        size_t origsize = wcslen(wch) + 1;
        const size_t newsize = 100;
        size_t convertedChars = 0;
        char nstring[newsize];
        wcstombs_s(&convertedChars, nstring, origsize, wch, _TRUNCATE);
        strcat_s(nstring, " (char *)");
        cout << nstring << endl;
    
        // Convert to a wchar_t*
        wchar_t wcstring[newsize];
        wcscpy_s(wcstring, wch);
        wcscat_s(wcstring, L" (wchar_t *)");
        wcout << wcstring << endl;
    
        // Convert to a _bstr_t
        _bstr_t bstrt(wch);
        bstrt += " (_bstr_t)";
        cout << bstrt << endl;
    
        // Convert to a CComBSTR
        CComBSTR ccombstr(wch);
        if (ccombstr.Append(L" (CComBSTR)") == S_OK)
        {
            CW2A printstr(ccombstr);
            cout << printstr << endl;
        }
    
        // Convert to a CString
        CString cstring(wch);
        cstring += " (CString)";
        cout << cstring << endl;
    
        // Convert to a basic_string
        wstring basicstring(wch);
        basicstring += L" (basic_string)";
        wcout << basicstring << endl;
    
        delete orig;
    }

    输出

    Hello, World! (System::String)
    Hello, World! (char *)
    Hello, World! (wchar_t *)
    Hello, World! (_bstr_t)
    Hello, World! (CComBSTR)
    Hello, World! (CString)
    Hello, World! (basic_string)
posted on 2006-12-14 14:22 清源游民 阅读(2339) 评论(2)  编辑 收藏 引用 所属分类: C++

FeedBack:
# re: 烦人的类型转换
2009-01-15 16:31 | gogoplayer
好文!  回复  更多评论
  
# re: 烦人的类型转换
2010-07-14 14:04 | 162212521@163.com
挺详细的 谢谢分享  回复  更多评论
  

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