How do I convert a char string to a wchar_t string?

Question

I have a string in char* format and would like to convert it to wchar_t*, to pass to a Windows function.

Solution 1

Does this little function help?

#include <cstdlib>

int mbstowcs(wchar_t *out, const char *in, size_t size);

Also see the C++ reference

Solution 2

If you don't want to link against the C runtime library, use the MultiByteToWideChar API call, e.g:

const size_t WCHARBUF = 100;
const char szSource[] = "HELLO";
wchar_t  wszDest[WCHARBUF];
MultiByteToWideChar(CP_ACP, MB_PRECOMPOSED, szSource, -1, wszDest, WCHARBUF);

Solution 3

the Windows SDK specifies 2 functions in kernel32.lib for converting strings from and to a wide character set. those are MultiByteToWideChar() and WideCharToMultiByte().

please note that, unlike the function name suggest, the string does not necessarily use a multi-byte character set, but can be a simple ANSI string. alse note that those functions understand UTF-7 and UTF-8 as a multi-byte character set. the wide char character set is always UTF-16.

Solution 4

schnaader's answer use the conversion defined by the current C locale, this one uses the C++ locale interface (who said that it was simple?)

std::wstring widen(std::string const& s, std::locale loc)
{
    std::char_traits<wchar_t>::state_type state = { 0 };

    typedef std::codecvt<wchar_t, char, std::char_traits<wchar_t>::state_type >
        ConverterFacet;

    ConverterFacet const& converter(std::use_facet<ConverterFacet>(loc));

    char const* nextToRead = s.data();
    wchar_t buffer[BUFSIZ];
    wchar_t* nextToWrite;
    std::codecvt_base::result result;
    std::wstring wresult;

    while ((result
            = converter.in
                  (state,
                   nextToRead, s.data()+s.size(), nextToRead,
                   buffer, buffer+sizeof(buffer)/sizeof(*buffer), nextToWrite))
           == std::codecvt_base::partial)
    {
        wresult.append(buffer, nextToWrite);
    }

    if (result == std::codecvt_base::error) {
        throw std::runtime_error("Encoding error");
    }
    wresult.append(buffer, nextToWrite);
    return wresult;
}

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Comments

[MSalters]

Most Windows functions actually come in two flavors, a "A" and "W" version. E.g. MessageBoxA / MessageBoxW, with a macro "MessageBox" refering to one of the two. But if you use the explicit MessageBoxA name, you can pass a char* independent of project settings.

[asveikau]

Depending on where your string comes from, you might also want to consider CP_UTF8 instead of CP_ACP. It can store all Unicode characters.

[netskink]

For me on windows10 with visual studio 2017, CP_ACP worked. CP_UTF8 did not.

[user2498772]

This function is deprecated.