Problems Inserting a CStringW into a std::wostringstream
c++, mfc, unicode, wostringstream
Solution
The wide character version of `operator<<` is a template and as such requires an exact argument match. No user-defined conversion, such as `CStringW::operator wchar_t*()` is implicitly performed.
OTOH the `void*` version of the same operator is not a template and happily uses the user-defined conversion operator.
Problem
I'm working on converting an MFC program from MBCS to Unicode. I've found that the insertion operator << is working differently with CStringA than with CStringW instances. ``` // char std::ostringstream c_oss; CStringA c_s("Hello"); c_oss << c_s; TRACE("%s\n", c_oss.str().c_str()); // wchar_t std::wostringstream w_oss; CStringW w_s(L"World"); w_oss << w_s; TRACE(L"%s\n", w_oss.str().c_str()); ``` I would expect this to print "Hello\nWorld\n" but instead it prints "Hello\n14,5E6,B38\n". That is, it's printing the address of the w_s data rather than the data. If I debug into w_oss << w_s, I can see that the overload for inserting a const void* is being selected rather than the one for inserting a const wchar_t*. It's working correctly for the char version. If I explicitly apply the case (LPCTSTR) or (const wchar_t*), it works correctly for the wchar_t version. Any ideas why the wchar_t version is working differently than the char version?