字符串转换 - 应该熟练掌握的东西

winston

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,但并不直直指向字串的缓冲区。    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。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

// 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  
// 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// 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
  // 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
  // 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
  #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// 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)源www.cnblogs.com/zhucl1006/archive/2008/01/04/1025959.html
  
  
  
  

earthdog

楼主说的这些其实很多都是不必要的，如果只是宽窄字符串之间的转化，而你使用的是MFC或者ATL的话，你可以只使用CString和CAtlString来实现（即使不是MFC或者ATL也可以只通过包含相应的文件来使用。至于楼主使用的CW2A和CA2W等，我不是太推荐，首先你需要多连接一个lib，需要进行设置，其次，如果你使用的是VC6和之前的版本的话，字符串太大的情况，会出现堆栈溢出的情况，（当然，楼主的是Managed C++，这种情况不会出现）。我的建议是采用系统函数：
WideCharToMultiByte
MultiByteToWideChar
希望能对楼主有所帮助。