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_Generic(3) Library Functions Manual _Generic(3)
_Generic - type-generic selection
_Generic(expression, type1: e1, ... /*, default: e */);
_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.
C11.
C11.
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);
}
Linux man-pages (unreleased) (date) _Generic(3)