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51 lines
2.2 KiB
C
51 lines
2.2 KiB
C
/* ignore a function return without a compiler warning. -*- coding: utf-8 -*-
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Copyright (C) 2008-2017 Free Software Foundation, Inc.
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This program is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>. */
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/* Written by Jim Meyering, Eric Blake and Pádraig Brady. */
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/* Use "ignore_value" to avoid a warning when using a function declared with
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gcc's warn_unused_result attribute, but for which you really do want to
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ignore the result. Traditionally, people have used a "(void)" cast to
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indicate that a function's return value is deliberately unused. However,
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if the function is declared with __attribute__((warn_unused_result)),
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gcc issues a warning even with the cast.
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Caution: most of the time, you really should heed gcc's warning, and
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check the return value. However, in those exceptional cases in which
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you're sure you know what you're doing, use this function.
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For the record, here's one of the ignorable warnings:
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"copy.c:233: warning: ignoring return value of 'fchown',
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declared with attribute warn_unused_result". */
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#ifndef _GL_IGNORE_VALUE_H
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#define _GL_IGNORE_VALUE_H
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/* Normally casting an expression to void discards its value, but GCC
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versions 3.4 and newer have __attribute__ ((__warn_unused_result__))
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which may cause unwanted diagnostics in that case. Use __typeof__
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and __extension__ to work around the problem, if the workaround is
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known to be needed. */
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#if 3 < __GNUC__ + (4 <= __GNUC_MINOR__)
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# define ignore_value(x) \
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(__extension__ ({ __typeof__ (x) __x = (x); (void) __x; }))
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#else
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# define ignore_value(x) ((void) (x))
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#endif
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#endif
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