79 lines
3.0 KiB
C
79 lines
3.0 KiB
C
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/* Close a stream, with nicer error checking than fclose's.
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Copyright (C) 1998-2002, 2004, 2006-2020 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 <https://www.gnu.org/licenses/>. */
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#include <config.h>
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#include "close-stream.h"
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#include <errno.h>
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#include <stdbool.h>
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#include "fpending.h"
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#if USE_UNLOCKED_IO
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# include "unlocked-io.h"
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#endif
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/* Close STREAM. Return 0 if successful, EOF (setting errno)
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otherwise. A failure might set errno to 0 if the error number
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cannot be determined.
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A failure with errno set to EPIPE may or may not indicate an error
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situation worth signaling to the user. See the documentation of the
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close_stdout_set_ignore_EPIPE function for details.
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If a program writes *anything* to STREAM, that program should close
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STREAM and make sure that it succeeds before exiting. Otherwise,
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suppose that you go to the extreme of checking the return status
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of every function that does an explicit write to STREAM. The last
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printf can succeed in writing to the internal stream buffer, and yet
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the fclose(STREAM) could still fail (due e.g., to a disk full error)
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when it tries to write out that buffered data. Thus, you would be
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left with an incomplete output file and the offending program would
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exit successfully. Even calling fflush is not always sufficient,
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since some file systems (NFS and CODA) buffer written/flushed data
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until an actual close call.
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Besides, it's wasteful to check the return value from every call
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that writes to STREAM -- just let the internal stream state record
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the failure. That's what the ferror test is checking below. */
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int
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close_stream (FILE *stream)
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{
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const bool some_pending = (__fpending (stream) != 0);
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const bool prev_fail = (ferror (stream) != 0);
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const bool fclose_fail = (fclose (stream) != 0);
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/* Return an error indication if there was a previous failure or if
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fclose failed, with one exception: ignore an fclose failure if
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there was no previous error, no data remains to be flushed, and
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fclose failed with EBADF. That can happen when a program like cp
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is invoked like this 'cp a b >&-' (i.e., with standard output
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closed) and doesn't generate any output (hence no previous error
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and nothing to be flushed). */
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if (prev_fail || (fclose_fail && (some_pending || errno != EBADF)))
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{
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if (! fclose_fail)
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errno = 0;
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return EOF;
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}
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return 0;
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}
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