1  /* ignore a function return without a compiler warning.  -*- coding: utf-8 -*-
       2  
       3     Copyright (C) 2008-2022 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