Question

We have a piece of cross-platform code that uses wide strings. All our string constants are wide strings and we need to use CFSTR() on some of them. We use these macros to get rid of L from wide strings:

// strip leading L"..." from wide string macros
// expand macro, e.g. turn WIDE_STRING (#define WIDE_STRING L"...") into L"..."
#  define WIDE2NARROW(WideMacro)     REMOVE_L(WideMacro)
// L"..." -> REM_L"..."
#  define REMOVE_L(WideString)       REM_##WideString
// REM_L"..." -> "..."
#  define REM_L

This works on both Windows and Linux. Not on Mac – we get the following error:

“error: pasting "REM_" and "L"qm"" does not give a valid preprocessing token”

Mac example:

#define TRANSLATIONS_DIR_BASE_NAME           L"Translations"
#define TRANSLATIONS_FILE_NAME_EXTENSION     L"qm"

CFURLRef appUrlRef = CFBundleCopyResourceURL( CFBundleGetMainBundle()
                                            , macTranslationFileName
                                            , CFSTR(WIDE2NARROW(TRANSLATIONS_FILE_NAME_EXTENSION))
                                            , CFSTR(WIDE2NARROW(TRANSLATIONS_DIR_BASE_NAME))
                                            );

Any ideas?

Answer 1

During tokenization, which happens before the preprocessor language, string literals are processed. So the L"qm" is converted to a wide string literal. Which means you are trying to token paste with a string literal(and not the letter L), which C99 forbids.