VC 中类型转换

转载：http://www.cnblogs.com/zhucl1006/archive/2008/01/04/1025959.html

CString－>TCHAR*的转化可以用函数GetBuff()

函数原型为：LPTSTR GetBuffer( int nMinBufLength );
CString str("CString");
TCHAR* szMsg = new TCHAR[100];
//其参数为CString字符串的长度
szMsg = str.GetBuffer(str.GetLength());
str.ReleaseBuffer();
delete []szMsg;
szMsg = NULL;

TCHAR*－>CString的转化

TCHAR szTchar[18] = L"TCHAR";
CString str;
str.Format(_T("%s"),szTchar);

CString和string的互相转换

CString->std::string 例子：

CString strMfc="test";

std::string strStl;

strStl=strMfc.GetBuffer(0);

std::string->CString 例子：

CString strMfc；

std::string strStl="test";

strMfc=strStl.c_str();

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_t、CComBSTR、CString、basic_string 和 System.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)