Compare std::wstring and std::string

Question

How can I compare a wstring, such as L\"Hello\", to a string? If I need to have the same type, how can I convert them into the same ty

Answer 1

Think twice before doing this — you might not want to compare them in the first place. If you are sure you do and you are using Windows, then convert string to wstring with MultiByteToWideChar, then compare with CompareStringEx.

If you are not using Windows, then the analogous functions are mbstowcs and wcscmp. The standard wide character C++ functions are often not portable under Windows; for instance mbstowcs is deprecated.

The cross-platform way to work with Unicode is to use the ICU library.

Take care to use special functions for Unicode string comparison, don't do it manually. Two Unicode strings could have different characters, yet still be the same.

wstring ConvertToUnicode(const string & str)
{
    UINT  codePage = CP_ACP;
    DWORD flags    = 0;
    int resultSize = MultiByteToWideChar
        ( codePage     // CodePage
        , flags        // dwFlags
        , str.c_str()  // lpMultiByteStr
        , str.length() // cbMultiByte
        , NULL         // lpWideCharStr
        , 0            // cchWideChar
        );
    vector result(resultSize + 1);
    MultiByteToWideChar
        ( codePage     // CodePage
        , flags        // dwFlags
        , str.c_str()  // lpMultiByteStr
        , str.length() // cbMultiByte
        , &result[0]   // lpWideCharStr
        , resultSize   // cchWideChar
        );
    return &result[0];
}