1  /* Detect write error on a stream.
       2     Copyright (C) 2003, 2005-2006, 2009-2023 Free Software Foundation, Inc.
       3     Written by Bruno Haible <bruno@clisp.org>, 2003.
       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  /* There are two approaches for detecting a write error on a stream opened
      19     for writing:
      20  
      21       (a) Test the return value of every fwrite() or fprintf() call, and react
      22           immediately.
      23       (b) Just before fclose(), test the error indicator in the stream and
      24           the return value of the final fclose() call.
      25  
      26     The benefit of (a) is that non file related errors (such that ENOMEM during
      27     fprintf) and temporary error conditions can be diagnosed accurately.
      28  
      29     A theoretical benefit of (a) is also that, on POSIX systems, in the case of
      30     an ENOSPC error, errno is set and can be used by error() to provide a more
      31     accurate error message. But in practice, this benefit is not big because
      32     users can easily figure out by themselves why a file cannot be written to,
      33     and furthermore the function fwriteerror() can provide errno as well.
      34  
      35     The big drawback of (a) is extensive error checking code: Every function
      36     which does stream output must return an error indicator.
      37  
      38     This file provides support for (b).  */
      39  
      40  #include <stdio.h>
      41  
      42  #ifdef __cplusplus
      43  extern "C" {
      44  #endif
      45  
      46  /* Write out the not yet written buffered contents of the stream FP, close
      47     the stream FP, and test whether some error occurred on the stream FP.
      48     FP must be a stream opened for writing.
      49     Return 0 if no error occurred and fclose (fp) succeeded.
      50     Return -1 and set errno if there was an error.  The errno value will be 0
      51     if the cause of the error cannot be determined.
      52     For any given stream FP other than stdout, fwriteerror (FP) may only be
      53     called once.  */
      54  extern int fwriteerror (FILE *fp);
      55  
      56  /* Likewise, but don't consider it an error if FP has an invalid file
      57     descriptor and no output was done to FP.  */
      58  extern int fwriteerror_no_ebadf (FILE *fp);
      59  
      60  #ifdef __cplusplus
      61  }
      62  #endif