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.\" Copyright (C) 2022 Alejandro Colomar <alx@kernel.org>
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.TH _Generic 3 2024-06-15 "Linux man-pages (unreleased)"
.SH NAME
_Generic \- type-generic selection
.SH SYNOPSIS
.nf
.BR _Generic( \fIexpression\fP ", type1: " e1 ", " "... /*" \
", default: " "e */" );
.fi
.SH DESCRIPTION
.BR _Generic ()
evaluates the path of code under the type selector
that is compatible with the type of the controlling
.IR expression ,
or
.B default:
if no type is compatible.
.P
.I expression
is not evaluated.
.P
This is especially useful for writing type-generic macros,
that will behave differently depending on the type of the argument.
.SH STANDARDS
C11.
.SH HISTORY
C11.
.SH EXAMPLES
The following program demonstrates how to write
a replacement for the standard
.BR imaxabs (3)
function, which being a function can't really provide what it promises:
seamlessly upgrading to the widest available type.
.IP
.\" SRC BEGIN (_Generic.c)
.EX
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
\&
#define my_imaxabs _Generic(INTMAX_C(0), \[rs]
long: labs, \[rs]
long long: llabs \[rs]
/* long long long: lllabs */ \[rs]
)
\&
int
main(void)
{
off_t a;
\&
a = \-42;
printf("imaxabs(%jd) == %jd\[rs]n", (intmax_t) a, my_imaxabs(a));
printf("&imaxabs == %p\[rs]n", &my_imaxabs);
printf("&labs == %p\[rs]n", &labs);
printf("&llabs == %p\[rs]n", &llabs);
\&
exit(EXIT_SUCCESS);
}
.EE
.\" SRC END
|
