C Macro Overloading by Argument List Length

Single header providing one macro allowing overloading of other macros based on number of passed arguments.

May be used for providing default argument values for functions.

Should work in C99, might work in C89 with some compiler extensions.

Usage

Choose prefix for overloading (may be the same as macro), then define:

#define macro(...) CMOBALL(prefix, __VA_ARGS__)

Then define macros using prefix_N(x1,x2,...,xN) notation (where N is number of taken arguments).

Examples

#include <stdio.h>
#include "cmoball.h"

int foo(int a, int b, int c)
{
    return a + b + c;
}

#define foo(...) CMOBALL(FOO, __VA_ARGS__)
#define FOO_3(x,y,z) foo(x,y,z)
#define FOO_2(x,y)   FOO_3(x,y,2)
#define FOO_1(x)     FOO_2(x,2)
#define FOO_0()      FOO_1(2)

int main()
{
    printf("%d\n", foo());      // 6
    printf("%d\n", foo(1));     // 5
    printf("%d\n", foo(1,1,1)); // 3

    return 0;
}

#include <stdio.h>
#include "cmoball.h"

int bar(int x, int b, int h)
{
    return 2+h;
}

#define bar_3(x,y,z) bar(x,y,z)
#define bar(...)     CMOBALL(bar, __VA_ARGS__) // no particular order needed
#define bar_2(x,y)   bar_3(x,y,0)

int main()
{
    printf("%d\n", bar(4,0));   // 2
    printf("%d\n", bar(4,1,1)); // 3
    // printf("%d\n", bar(1));  // error

    return 0;
}

#include <stdio.h>
#include "cmoball.h"

#define NoA(...) CMOBALL(FOO, __VA_ARGS__)
#define FOO_3(x,y,z) "Three"
#define FOO_2(x,y)   "Two"
#define FOO_1(x)     "One"
#define FOO_0()      "Zero"


int main()
{
    puts(NoA());
    puts(NoA(1));
    puts(NoA(1,1));
    puts(NoA(1,1,1));
    return 0;
}