1 /* ignore a function return without a compiler warning. -*- coding: utf-8 -*- 2 3 Copyright (C) 2008-2020 Free Software Foundation, Inc. 4 5 This program is free software: you can redistribute it and/or modify 6 it under the terms of the GNU General Public License as published by 7 the Free Software Foundation; either version 3 of the License, or 8 (at your option) any later version. 9 10 This program 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 General Public License for more details. 14 15 You should have received a copy of the GNU 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 #if 3 < __GNUC__ + (4 <= __GNUC_MINOR__) 44 # define ignore_value(x) \ 45 (__extension__ ({ __typeof__ (x) __x = (x); (void) __x; })) 46 #else 47 # define ignore_value(x) ((void) (x)) 48 #endif 49 50 #endif 51