方式一：采用ATL封装_bstr_t的过渡

#include <comutil.h>  
#pragma comment(lib, "comsuppw.lib")
 
string wstring2string(const wstring& ws)
{
    _bstr_t t = ws.c_str();  
    char* pchar = (char*)t;  
    string result = pchar;  
    return result;  
}
 
wstring string2wstring(const string& s)
{
    _bstr_t t = s.c_str();  
    wchar_t* pwchar = (wchar_t*)t;  
    wstring result = pwchar;  
    return result; 
}

方式二：调用Windows API

#include <Windows.h>
//将string转换成wstring  
wstring string2wstring(string str)  
{  
    wstring result;  
    //获取缓冲区大小，并申请空间，缓冲区大小按字符计算  
    int len = MultiByteToWideChar(CP_ACP, 0, str.c_str(), str.size(), NULL, 0);  
    TCHAR* buffer = new TCHAR[len + 1];  
    //多字节编码转换成宽字节编码  
    MultiByteToWideChar(CP_ACP, 0, str.c_str(), str.size(), buffer, len);  
    buffer[len] = '\0';             //添加字符串结尾  
    //删除缓冲区并返回值  
    result.append(buffer);  
    delete[] buffer;  
    return result;  
}  
  
//将wstring转换成string  
string wstring2string(wstring wstr)  
{  
    string result;  
    //获取缓冲区大小，并申请空间，缓冲区大小事按字节计算的  
    int len = WideCharToMultiByte(CP_ACP, 0, wstr.c_str(), wstr.size(), NULL, 0, NULL, NULL);  
    char* buffer = new char[len + 1];  
    //宽字节编码转换成多字节编码  
    WideCharToMultiByte(CP_ACP, 0, wstr.c_str(), wstr.size(), buffer, len, NULL, NULL);  
    buffer[len] = '\0';  
    //删除缓冲区并返回值  
    result.append(buffer);  
    delete[] buffer;  
    return result;  
}

方式三：使用CRT库的mbstowcs()函数和wcstombs()函数，平台无关，需设定locale。（运行速度巨慢）

#include <string>
#include <locale.h>
using namespace std;
string ws2s(const wstring& ws)
{
string curLocale = setlocale(LC_ALL, NULL); // curLocale = "C";
 
setlocale(LC_ALL, "chs");
 
const wchar_t* _Source = ws.c_str();
size_t _Dsize = 2 * ws.size() + 1;
char *_Dest = new char[_Dsize];
memset(_Dest,0,_Dsize);
wcstombs(_Dest,_Source,_Dsize);
string result = _Dest;
delete []_Dest;
 
setlocale(LC_ALL, curLocale.c_str());
 
return result;
}
 
wstring s2ws(const string& s)
{
setlocale(LC_ALL, "chs");
 
const char* _Source = s.c_str();
size_t _Dsize = s.size() + 1;
wchar_t *_Dest = new wchar_t[_Dsize];
wmemset(_Dest, 0, _Dsize);
mbstowcs(_Dest,_Source,_Dsize);
wstring result = _Dest;
delete []_Dest;
 
setlocale(LC_ALL, "C");
 
return result;
}