How to use __VA_ARGS__ inside a C function instead of macro? [duplicate]

Question

Possible Duplicate:
C/C++: Passing variable number of arguments around

I'm currently using the following macro declared on my C file.

#define COMMON_Print(...) printf (__VA_ARGS__) 

Now that call works just fine, but turns out that I need to be able to create a C function that looks something like this:

void COMMON_Print(...) {         printf (__VA_ARGS__); } 

So that function doesn't work, I get an error

"Error : undefined identifier __VA_ARGS__"

The complexity of my project requires to have a function since it's an interface... So how can I get the parameters ... and pass them to the printf function? Or better what am I doing wrong?

Thanks!

Answer 1

Each of the ?printf functions has a corresponding v?printf function which does the same thing but takes a va_list, a variable argument list.

#include <stdio.h> #include <stdarg.h>  void COMMON_Print(char *format, ...) {     va_list args;      va_start(args, format);     vprintf(format, args);     va_end(args); } 

Side note: Notice that va_start takes the name of the last argument before the ... as a parameter. va_start is a macro which does some stack-based magic to retrieve the variable arguments and it needs the address of the last fixed argument to do this.

As a consequence of this, there has to be at least one fixed argument so you can pass it to va_start. This is why I added the format argument instead of sticking with the simpler COMMON_Print(...) declaration.

See: http://www.cplusplus.com/reference/clibrary/cstdio/vprintf/