Name
_Generic - type-generic selectionSynopsis
_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 controllingexpression
, 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.History
C11.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), \e long: labs, \e long long: llabs \e /* long long long: lllabs */ \e ) int main(void) { off_t a; a = -42; printf("imaxabs(%jd) == %jd\en", (intmax_t) a, my_imaxabs(a)); printf("&imaxabs == %p\en", &my_imaxabs); printf("&labs == %p\en", &labs); printf("&llabs == %p\en", &llabs); exit(EXIT_SUCCESS); }