C11 宽字节转为多字节实现

BOOL WStringToString(const std::wstring &wstr,std::string &str)
{   
typedef std::codecvt<wchar_t,char,std::mbstate_t> convert_facet;
std::locale mylocale;
const convert_facet& myfacet = std::use_facet<convert_facet>(mylocale);
size_t length_ = wstr.length();
std::unique_ptr<char> pstr(new char[length_+1]);
std::mbstate_t mbs = std::mbstate_t();
const wchar_t* pwc;
char* pc;
convert_facet::result myresult = myfacet.out(mbs,wstr.c_str(),wstr.c_str()+length_+1,pwc,pstr.get(),pstr.get()+length_+1,pc);
if (myresult != convert_facet::ok)
return FALSE;
str = pstr.get();
return TRUE;
}