1 /* ignore a function return without a compiler warning. -*- coding: utf-8 -*-
2
3 Copyright (C) 2008-2023 Free Software Foundation, Inc.
4
5 This file is free software: you can redistribute it and/or modify
6 it under the terms of the GNU Lesser General Public License as
7 published by the Free Software Foundation; either version 2.1 of the
8 License, or (at your option) any later version.
9
10 This file is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 GNU Lesser General Public License for more details.
14
15 You should have received a copy of the GNU Lesser General Public License
16 along with this program. If not, see <https://www.gnu.org/licenses/>. */
17
18 /* Written by Jim Meyering, Eric Blake and Pádraig Brady. */
19
20 /* Use "ignore_value" to avoid a warning when using a function declared with
21 gcc's warn_unused_result attribute, but for which you really do want to
22 ignore the result. Traditionally, people have used a "(void)" cast to
23 indicate that a function's return value is deliberately unused. However,
24 if the function is declared with __attribute__((warn_unused_result)),
25 gcc issues a warning even with the cast.
26
27 Caution: most of the time, you really should heed gcc's warning, and
28 check the return value. However, in those exceptional cases in which
29 you're sure you know what you're doing, use this function.
30
31 For the record, here's one of the ignorable warnings:
32 "copy.c:233: warning: ignoring return value of 'fchown',
33 declared with attribute warn_unused_result". */
34
35 #ifndef _GL_IGNORE_VALUE_H
36 #define _GL_IGNORE_VALUE_H
37
38 /* Normally casting an expression to void discards its value, but GCC
39 versions 3.4 and newer have __attribute__ ((__warn_unused_result__))
40 which may cause unwanted diagnostics in that case. Use __typeof__
41 and __extension__ to work around the problem, if the workaround is
42 known to be needed.
43 The workaround is not needed with clang. */
44 #if (3 < __GNUC__ + (4 <= __GNUC_MINOR__)) && !defined __clang__
45 # define ignore_value(x) \
46 (__extension__ ({ __typeof__ (x) __x = (x); (void) __x; }))
47 #else
48 # define ignore_value(x) ((void) (x))
49 #endif
50
51 #endif