对有关数据类型转换的整理

烦人的类型转换

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)