std::string 与 std::wstring 转换方法的效率比较

// Calls the provided work function and returns the number of milliseconds // that it takes to call that function.template <class Function>__int64 time_call(Function&& f){    __int64 begin = GetTickCount64();    f();    return GetTickCount64() - begin;}// Use WideCharToMultiByte and MultiByteToWideCharstring WChar2Ansi(const wchar_t* pwszSrc){    int nLen = WideCharToMultiByte(CP_ACP, 0, pwszSrc, -1, NULL, 0, NULL, NULL);         if (nLen<= 0) return string("");    char* pszDst = new char[nLen];    if (NULL == pszDst) return string("");    WideCharToMultiByte(CP_ACP, 0, pwszSrc, -1, pszDst, nLen, NULL, NULL);    pszDst[nLen -1] = 0;    string strTemp(pszDst);    delete [] pszDst;    return strTemp;}wstring Ansi2WChar(const char* pszSrc, int nLen){    int nSize = MultiByteToWideChar(CP_ACP, 0, pszSrc, nLen, 0, 0);    if(nSize <= 0) return NULL;    wchar_t *pwszDst = new wchar_t[nSize+1];    if( NULL == pwszDst) return NULL;    MultiByteToWideChar(CP_ACP, 0, pszSrc, nLen, pwszDst, nSize);    pwszDst[nSize] = 0;    if( pwszDst[0] == 0xFEFF)                    // skip Oxfeff        for(int i = 0; i < nSize; i ++)             pwszDst[i] = pwszDst[i+1];     wstring wcharString(pwszDst);    delete pwszDst;    return wcharString;}// Use wcstombs_s and mbstowcs_s string ws2s(wstring ws){    const wchar_t* Source = ws.c_str();    size_t size = 2 * ws.size() + 1;    char* Dest = new char[size];    memset(Dest,0, size);    size_t len = 0;    wcstombs(Dest, Source, size);    //wcstombs_s(&len, Dest, size, Source, size);    string result = Dest;    delete [] Dest;    return result;}wstring s2ws(string s){    const char* Source = s.c_str();    size_t size = s.size() + 1;    wchar_t* Dest = new wchar_t[size];    wmemset(Dest, 0, size);    size_t len = 0;    mbstowcs(Dest, Source, size);    //mbstowcs_s(&len, Dest, size, Source, size);    wstring result = Dest;    delete [] Dest;    return result;}// Testing     __int64 elapsed;    string input = "Hello, World.\\XXX\\XXX";    wstring winput = L"Hello, World.\\XXX\\XXX";    wchar_t dest[1000];    int count = 10000;    elapsed = time_call([input, &count]     {        while (count)        {            Ansi2WChar(input.c_str(), input.length());            count--;        }    });    memset(dest, 0, 1000);    _itow_s(elapsed, dest, 10);    OutputDebugStringW(L"Time:");    OutputDebugStringW(dest);    OutputDebugStringW(L"ms\n");    count = 10000;    elapsed = 0;    elapsed = time_call([input, &count]     {        while (count)        {            s2ws(input);            count--;        }    });    memset(dest, 0, 1000);    _itow_s(elapsed, dest, 10);    OutputDebugStringW(L"Time:");    OutputDebugStringW(dest);    OutputDebugStringW(L"ms\n");    count = 10000;    elapsed = 0;    elapsed = time_call([winput, &count]     {        while (count)        {            WChar2Ansi(winput.c_str());            count--;        }    });    memset(dest, 0, 1000);    _itow_s(elapsed, dest, 10);    OutputDebugStringW(L"Time:");    OutputDebugStringW(dest);    OutputDebugStringW(L"ms\n");    count = 10000;    elapsed = 0;    elapsed = time_call([winput, &count]     {        while (count)        {            ws2s(winput);            count--;        }    });    memset(dest, 0, 1000);    _itow_s(elapsed, dest, 10);    OutputDebugStringW(L"Time:");    OutputDebugStringW(dest);    OutputDebugStringW(L"ms\n");

输出：

Time:78ms

Time:94ms

Time:62ms

Time:109ms

从输出结果可以看出

WideCharToMultiByte和 MultiByteToWideChar转换效率要比 mbstowcs和wcstombs高。

注意：如果使用mbstowcs则需要Disable Specific Warnings： 4996