Qt using std::use_facet with wstring

Question

I need crossplatform code to skip leading spaces for wide string. It's looking that g++ (and Qt obviously) doesn't initialize slots for wide string at all So following code works fine for VC++ but almost g++ fails with bad_cast exception:

#include <string>
#include <locale>
#include <iostream>

int main()
{
    typedef std::ctype<std::wstring::value_type> vtct;
    std::wstring str=L"      1122";
    const std::wstring::value_type* unspace = 
        std::use_facet<vtct>( std::locale::classic() ).
            scan_not(std::ctype_base::space|std::ctype_base::punct, 
            str.c_str(), str.c_str() + str.length());
   //std::cout << unspace << std::endl;
   wprintf(L"{%s}\n", unspace);
   return 0;
}

According to spec: *"bad_cast exception when the facet repository in the locale object contains no facet with the requested locale::id"*

So general question how g++ deals with wide string? More narrow question - how to initialize facets at least for ctype?

Update: after some experiments, I've detected that linux g++ correctly initializes facet for wide string - so code works. Obviously described problem is feature if mingw only.

Answer 1

I try not to use the STL localization support because:

• it is complicated
• as far as I can tell, compiler support is not so good.

Since you have mentioned Qt, you can try to create a QString from the wstring and verify what chars are spaces with QChar::isSpace.

See this resource for more help with C++ localization. It includes a link to B.Stroustrup's appendix about localization.

Answer 2

Are you using MingGW? Their stable version don't support wchar_t.

I use C++ wide character support (facets too) in g++ on Linux without any trouble.

I had to make my code support narrow-character-only compilation mode to work with MinGW though.