_Generic

Section: C Library Functions (3)
Updated: 2023-02-12
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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); }

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Time: 14:08:27 GMT, May 18, 2024