| 1 | /* ignore a function return without a compiler warning. -*- coding: utf-8 -*-
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| 2 |
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| 3 | Copyright (C) 2008-2021 Free Software Foundation, Inc.
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| 4 |
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| 5 | This file is free software: you can redistribute it and/or modify
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| 6 | it under the terms of the GNU Lesser General Public License as
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| 7 | published by the Free Software Foundation; either version 2.1 of the
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| 8 | License, or (at your option) any later version.
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| 9 |
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| 10 | This file is distributed in the hope that it will be useful,
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| 11 | but WITHOUT ANY WARRANTY; without even the implied warranty of
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| 12 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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| 13 | GNU Lesser General Public License for more details.
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| 14 |
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| 15 | You should have received a copy of the GNU Lesser General Public License
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| 16 | along with this program. If not, see <https://www.gnu.org/licenses/>. */
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| 17 |
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| 18 | /* Written by Jim Meyering, Eric Blake and Pádraig Brady. */
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| 19 |
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| 20 | /* Use "ignore_value" to avoid a warning when using a function declared with
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| 21 | gcc's warn_unused_result attribute, but for which you really do want to
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| 22 | ignore the result. Traditionally, people have used a "(void)" cast to
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| 23 | indicate that a function's return value is deliberately unused. However,
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| 24 | if the function is declared with __attribute__((warn_unused_result)),
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| 25 | gcc issues a warning even with the cast.
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| 26 |
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| 27 | Caution: most of the time, you really should heed gcc's warning, and
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| 28 | check the return value. However, in those exceptional cases in which
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| 29 | you're sure you know what you're doing, use this function.
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| 30 |
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| 31 | For the record, here's one of the ignorable warnings:
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| 32 | "copy.c:233: warning: ignoring return value of 'fchown',
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| 33 | declared with attribute warn_unused_result". */
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| 34 |
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| 35 | #ifndef _GL_IGNORE_VALUE_H
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| 36 | #define _GL_IGNORE_VALUE_H
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| 37 |
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| 38 | /* Normally casting an expression to void discards its value, but GCC
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| 39 | versions 3.4 and newer have __attribute__ ((__warn_unused_result__))
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| 40 | which may cause unwanted diagnostics in that case. Use __typeof__
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| 41 | and __extension__ to work around the problem, if the workaround is
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| 42 | known to be needed.
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| 43 | The workaround is not needed with clang. */
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| 44 | #if (3 < __GNUC__ + (4 <= __GNUC_MINOR__)) && !defined __clang__
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| 45 | # define ignore_value(x) \
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| 46 | (__extension__ ({ __typeof__ (x) __x = (x); (void) __x; }))
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| 47 | #else
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| 48 | # define ignore_value(x) ((void) (x))
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| 49 | #endif
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| 50 |
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| 51 | #endif
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