C preprocessor: How to create a character literal?

Question

Just out of curiosity, I\'d like to know if it is possible to define a macro which can turn its argument into a character literal:

 switch(getchar()) {
   ca         


        

Answer 1

Here's my possible solution:

#define EVAL(...) __VA_ARGS__
#define Q() '
#define MYMACRO(...) Q()EVAL(__VA_ARGS__)Q()

(Variadic macros are used to to support MYMACRO(,) because it would be parsed as two empty arguments.)

I'm not sure if this code is standard-conformant due to the unmatched '. Still, I think this code works on most C99 compilers. However, this code does not work for the following characters:

• ( which has to match with )
• ) used to identify the start and end of the argument list
• ' and " used for string literals and character constants
• \, which needs escaping
• Whitespace characters, because they are not tokens

I'm fairly sure that there's no solution that work for (, ), ' or ", because if this was allowed, the compiler would have to change the way macros arguments are parsed.