variadic-macros

After reading about VA_NARG I tried to implement function overloading depending on number of arguments in C using macros. Now the problem is: void hello1(char *s) { ... } void hello2(char *s, char *t) { ... } // PP_NARG(...) macro returns number of arguments :ref to link above // does not work #define hello(...) hello ## PP_NARG(__VA_ARGS__) int main(void) { hello("hi"); // call hello1("hi"); hello("foo","bar"); // call hello2("foo","bar"); return 0; } I've read this from C-faq. But still could not get it to work... Jens Gustedt This is because of the evaluation rules for macros. You would

Is it legal to invoke a variadic macro M with no arguments for its variadic parameter? The relevant standard quote is [cpp.replace]/4 : If the identifier-list in the macro definition does not end with an ellipsis, the number of arguments (including those arguments consisting of no preprocessing tokens) in an invocation of a function-like macro shall equal the number of parameters in the macro definition. Otherwise, there shall be more arguments in the invocation than there are parameters in the macro definition (excluding the ... ). There shall exist a ) preprocessing token that terminates the

I'm trying to overload a macro by the number of parameter. Of course I can't actually overload the macro. I've tried using variadic macros to choose the right macro (using the fact that if __VA_ARGS__ doesn't exist it's supposed to delete the last coma before it - GCC Reference ): #define TEST1() printf("TEST1"); #define TEST2() printf("TEST2"); #define CHOOSER(x, y,FUNC,...) FUNC() #define MANIMACRO(...) CHOOSER(,__VA_ARGS__,TEST1,TEST2) int main(void) { MANIMACRO(1); MANIMACRO(); } The idea was that if __VA_ARGS__ exists it should pass 4 arguments to CHOOSER , where the third one should have

How can one define a C macro IFARGS(YES, NO, ...) such that invoking IFARGS with no additional arguments produces NO , and invoking IFARGS with one or more arguments produces YES ? I have an answer using GCC (see below), but I'd prefer one for C99 if possible (or a proof of its impossibility). In C99 it is possible to detect if a macro argument is empty, but making that robust against all odds that may appear in that argument (arguments that are themselves expanding, contain () and stuff like that) is difficult. My macro package P99 implements such a thing, so you wouldn't have to worry too

I found a question showing how to overload macros based on the number of arguments : Overloading Macro on Number of Arguments But as they say, it's not working using MSVC because MSVC expands __VA_ARGS__ into a single token instead of a list of arguments ( arg1, arg2, arg3 ). They point to another question where a work around is given : MSVC doesn't expand __VA_ARGS__ correctly But not explained at all, so I can't adapt it to my own case since I can't understand it. Could you please explain how this workaround works ? The workaround in question is this: #define EXPAND( x ) x #define F(x, ...)

I have been trying to implement a function macro in C that prepends "DEBUG: ", to the argument, and passes its arguments to printf: #define DBG(format, ...) printf("DEBUG: " #format "\n", __VA_ARGS__) This gives me this error in gcc: src/include/debug.h:4:70: error: expected expression before ‘)’ token #define DBG(format, ...) printf("DEBUG: " #format "\n", __VA_ARGS__) ^ Supposedly, it should stringise format, and pass its variable arguments to printf, but so far I can't get past this error. EDIT After giving up on stringising arguments, and double-hashing ( ## ) __VA_ARGS__ I now have this