_Generic(3)

NAME
_Generic - type-generic selection

SYNOPSIS
_Generic(expression, type1: e1, ... /*, default: e */);

DESCRIPTION
_Generic() evaluates the path of code under the type selector that is compatible with the type of the controlling expression, or default: if no type is compatible.

expression is not evaluated.

This is especially useful for writing type-generic macros, that will behave differently depending on the type of the argument.

STANDARDS
C11 and later.

EXAMPLES
The following program demonstrates how to write a replacement for the standard imaxabs(3) function, which being a function can't really provide what it promises: seamlessly upgrading to the widest available type.

        #include <stdint.h>
        #include <stdio.h>
        #include <stdlib.h>
        #define my_imaxabs  _Generic(INTMAX_C(0),  \
            long:           labs,                  \
            long long:      llabs                  \
         /* long long long: lllabs */              \
        )
        int
        main(void)
        {
            off_t  a;
            a = -42;
            printf("imaxabs(%jd) == %jd\n", (intmax_t) a, my_imaxabs(a));
            printf("&imaxabs == %p\n", &my_imaxabs);
            printf("&labs    == %p\n", &labs);
            printf("&llabs   == %p\n", &llabs);
            exit(EXIT_SUCCESS);
        }