How do I convert a char string to a wchar_t string? - c++

Question

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

Answer 1

Does this little function help?
#include <cstdlib>
int mbstowcs(wchar_t *out, const char *in, size_t size);
Also see the C++ reference

Answer 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);

Answer 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.

Answer 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;
}