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

You should convert the char string to a wchar_t string using mbstowcs, and then compare the resulting strings. Notice that mbstowcs works on char */wchar *, so you'll probably need to do something like this:

std::wstring StringToWstring(const std::string & source)
{
    std::wstring target(source.size()+1, L' ');
    std::size_t newLength=std::mbstowcs(&target[0], source.c_str(), target.size());
    target.resize(newLength);
    return target;
}

I'm not entirely sure that that usage of &target[0] is entirely standard-conforming, if someone has a good answer to that please tell me in the comments. Also, there's an implicit assumption that the converted string won't be longer (in number of wchar_ts) than the number of chars of the original string - a logical assumption that still I'm not sure it's covered by the standard.

On the other hand, it seems that there's no way to ask to mbstowcs the size of the needed buffer, so either you go this way, or go with (better done and better defined) code from Unicode libraries (be it Windows APIs or libraries like iconv).

Still, keep in mind that comparing Unicode strings without using special functions is slippery ground, two equivalent strings may be evaluated different when compared bitwise.

Long story short: this should work, and I think it's the maximum you can do with just the standard library, but it's a lot implementation-dependent in how Unicode is handled, and I wouldn't trust it a lot. In general, it's just better to stick with an encoding inside your application and avoid this kind of conversions unless absolutely necessary, and, if you are working with definite encodings, use APIs that are less implementation-dependent.