Home/ Questions/Q 8599989
In Process

The Archive Base Latest Questions

Editorial Team
  • 0
Asked: 2026-06-12T01:31:02+00:00

How would you write a variadic macro that can take either 1 or 0

  • 0

How would you write a variadic macro that can take either 1 or 0 arguments. I.e. something like this:

GREET()         // returns @"Hello World"
GREET(@"John")  // returns @"Hello John"
Share

Leave an answer

You must login to add an answer.

Need An Account,

1 Answer

  1. Editorial Team

    It’s quite simple, you have something like this:

    #define __NARGS(unused, _1, _2, _3, _4, _5, VAL, ...) VAL
#define NARGS(...) __NARGS(unused, ## __VA_ARGS__, 5, 4, 3, 2, 1, 0)

#define __GREET(ARGC, ARGS...) GREET_ ## ARGC (ARGS)
#define _GREET(ARGC, ARGS...) __GREET(ARGC, ARGS)
#define GREET(...) _GREET(NARGS(__VA_ARGS__), __VA_ARGS__)

#define GREET_0(...) @"Hello World!"
#define GREET_1(ARG, ...) @"Hello, " ARG // strings are auto-concatenated in objc

int main()
{
    NSLog(@"%@", GREET());
    NSLog(@"%@", GREET(@"John"));
}

    Output:

    2012-09-30 11:56:48.478 TestProj[51823:303] Hello World!
2012-09-30 11:56:48.480 TestProj[51823:303] Hello, John

    Now, this is quite complex, but assuming you understand at a basic level how the preprocessor works, you should be in a good position to understand what is happening.

    • 0