Question

Ive got a multi platform project that compiles great on mac, but on windows all my swprintf calls with a %s are looking for a wchar_t instead of the char * im passing it. Turns out M$ thought it would be funny to make %s stand for something other than char * in wide character functions… http://msdn.microsoft.com/en-us/library/hf4y5e3w.aspx

Anyways I’m looking for a creative coding trick thats better than putting ifdef else ends around every wide string call

Answer 1

Update: VS 2015 CTP6 reverted the changes and Microsoft are yet again acting different to the standard.

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Visual Studio 14 CTP1 and later will always treat %s as a narrow string (char*) unless you define _CRT_STDIO_LEGACY_WIDE_SPECIFIERS. It also added the T length modifier extension which maps to what MS calls the “natural” width. For sprintf %Ts is char* and for swprintf %Ts is wchar_t*.

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In Visual Studio 13 and earlier %s/%c is mapped to the natural width of the function/format string and %S/%C is mapped to the opposite of the natural with:

printf("%c %C %s %S\n", 'a', L'B', "cd", L"EF");
wprintf(L"%c %C %s %S\n", L'a', 'B', L"cd", "EF");

You can also force a specific width by using a length modifier: %ls, %lc, %ws and %wc always mean wchar_t and %hs and %hc are always char. (Documented for VS2003 here and VC6 here (Not sure about %ws and when it was really added))

Mapping %s to the natural width of the function was really handy back in the days of Win9x vs. WinNT, by using the tchar.h header you could build narrow and wide releases from the same source. When _UNICODE is defined the functions in tchar.h map to the wide functions and TCHAR is wchar_t, otherwise the narrow functions are used and TCHAR is char:

_tprintf(_T("%c %s\n"), _T('a'), _T("Bcd"));

There is a similar convention used by the Windows SDK header files and the few format functions that exist there (wsprintf, wvsprintf, wnsprintf and wvnsprintf) but they are controlled by UNICODE and TEXT and not _UNICODE and _T/_TEXT.

You probably have 3 choices to make a multi-platform project work on Windows if you want to support older Windows compilers:

1) Compile as a narrow string project on Windows, probably not a good idea and in your case swprintf will still treat %s as wchar_t*.

2) Use custom defines similar to how inttypes.h format strings work:

#ifdef _WIN32
#define PRIs "s"
#define WPRIs L"hs"
#else
#define PRIs "s"
#define WPRIs L"s" 
#endif
printf("%" PRIs " World\n", "Hello");
wprintf(L"%" WPRIs L" World\n", "Hello");

3) Create your own custom version of swprintf and use it with Visual Studio 13 and earlier.