Macro that can take variable qty of arguments

If you're using gcc, you can simply

#define DEBUG_OUTPUT(...) print_debug(...)

This won't work with other compilers, though...

#ifdef DEBUG
#define DEBUG_OUTPUT MyPrintf
#else
#define DEBUG_OUTPUT EmptyPrint
#endif



#include <stdio.h>
#include <stdarg.h>

void MyPrintf( char *s, ... )
{
}

void MyPrintf( char *s, ... )
{
va_list argList;
char msg[3000];

va_start( argList, s );
vsprintf( msg, s, argList);
va_end( argList );

printf("%s\n", msg );

}

int main()
{

    MyPrintf("%s %d", "Hello", 123);
    return 1;
}

BTW, just in case you weren't already aware of that: No other compiuler supports the construct of a 'macro taking a variable number of arguments', so you will eventually either end up having to use a function to perform that or use multiple macros that take account of the number of arguments you're passing, e.g. like

#ifdef DEBUG
#define DEBUG_OUTPUT1(d1) print_debug(d1)
#define DEBUG_OUTPUT2(d1, d2) print_debug(d1, d2)
// etc.pp.
#else
//...
#endif

thienpnguyen, your suggestion still involves an 'unnecessary' function call - and, BTW, I'd personally make it read

void MyPrintf( char *s, ... )
{
#ifdef DEBUG
//...
#endif
}

>>your suggestion still involves an 'unnecessary' function call

Which isn't really too bad, actually :o)

FYI:
The VC method does have one bad side effect.
Example:

//This works OK
void function_x(int xyz)
{
  DEBUG_PRINT("function_x(%i)", xyz);
  printf("Hello World");
}

//This will NOT works OK
void function_x(int xyz)
{
  if (xyz == 123) DEBUG_PRINT("function_x(%i)", xyz);
  printf("Hello World");
}

In NON-Debug mode, the compiler will see the second code like this:
if (xyz == 123) printf("Hello World");

You don't have this problem with the GNUC method.

jkr,
I tried your gcc method, but it failed to compile.
It seems like the correct syntax is the one posted by Axter.

Axter,
I tried your macro, and much to my surprise, it works on all the compilers I tested.  I did modify it a little.

#ifdef DEBUG
#ifdef __GNUC__
#define DEBUG_OUTPUT(args...) print_debug(args)
#else
#define DEBUG_OUTPUT print_debug
#endif //__GNUC__
#else  
#ifdef __GNUC__
#define DEBUG_OUTPUT(args...)
#else
#define DEBUG_OUTPUT ;/##/
#endif //__GNUC__
#endif //DEBUG

I added ";" before /##/
This will remove the bad side effect you posted.  The only down side to this modification is that it produces a warning on some compilers.  But I rather get the warning then to have the side effects.

Just out of curiousity, what compilers did you test it on?

I tested it in Visual C++ 6.0, Window/DOS GNU compiler, Borland (BC4), C++ Builder 5, Turbo C++ 3.0 and 4.5

With the modification I made, it gave a warning in Turbo C++ 3.0 and 4.5