How to define macro function which support no input parameter and support also input parametr in the same time

Question

I want to define a macro function which support at the same time:

1) No input parameter

2) Input parameters

some thing like that:

#de         


        

Answer 1

You can use sizeof for this purpose.

Consider something like this:

#define MACRO_TEST(X) { \
  int args[] = {X}; \
  printf("this is a test\n");\
  if(sizeof(args) > 0) \
    printf("%d\n",*args); \
}

Answer 2

Not exactly that but ...

#include <stdio.h>

#define MTEST_
#define MTEST__(x) printf("%d\n",x)
#define MACRO_TEST(x)\
    printf("this is a test\n");\
    MTEST_##x    

int main(void)
{
    MACRO_TEST();
    MACRO_TEST(_(5));
    return 0;
}

EDIT

And if 0 can be used as skip:

#include <stdio.h>

#define MACRO_TEST(x) \
    do { \
        printf("this is a test\n"); \
        if (x +0) printf("%d\n", x +0); \
    } while(0)

int main(void)
{
    MACRO_TEST();
    MACRO_TEST(5);
    return 0;
}

Answer 3

The C99 standard says,

An identifier currently defined as an object-like macro shall not be redefined by another #define reprocessing directive unless the second definition is an object-like macro definition and the two replacement lists are identical. Likewise, an identifier currently defined as a function-like macro shall not be redefined by another #define preprocessing directive unless the second definition is a function-like macro definition that has the same number and spelling of parameters, and the two replacement lists are identical.

I think compiler prompts a warning of redefined MACRO. Hence it is not possible.

Answer 4

gcc and recent versions of MS compilers support variadic macros - that is macros that work similar to printf.

gcc documentation here: http://gcc.gnu.org/onlinedocs/gcc/Variadic-Macros.html

Microsoft documentation here: http://msdn.microsoft.com/en-us/library/ms177415(v=vs.80).aspx