1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
|
.\" Copyright (C) 2022 Alejandro Colomar <alx@kernel.org>
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.TH _Generic 3 2023-02-12 "Linux man-pages 6.03"
.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.
.PP
.I expression
is not evaluated.
.PP
This is especially useful for writing type-generic macros,
that will behave differently depending on the type of the argument.
.SH STANDARDS
C11 and later.
.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), \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);
}
.EE
.\" SRC END
|
