C语言 函数默认参数

#include <stdio.h>

#define DEFARG(name, defval) ((#name[0]) ? (name + 0 ) : defval)

int _f1(int i)
{
return 2 * i;
}
#define f1(arg0) _f1(DEFARG(arg0, 0))

int _f2(int i, int j)
{
return i + j;
}
#define f2(arg0, arg1) _f2(DEFARG(arg0, 0), DEFARG(arg1, 1))

int main()
{
printf("%d\n", f1());
printf("%d\n", f1(1));
printf("%d\n", f2(, ));
printf("%d\n", f2(2, ));
printf("%d\n", f2(, 3));
printf("%d\n", f2(4, 5));
return 0;
}