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377e9733b5
As discussed in bug 5994 (plus duplicates), POSIX requires fflush after ungetc to discard pushed-back characters but preserve the file position indicator. For this purpose, each ungetc decrements the file position indicator by 1; it is unspecified after ungetc at the start of the file, and after ungetwc, so no special handling is needed for either of those cases. This is fixed with appropriate logic in _IO_new_file_sync. I haven't made any attempt to test or change things in this area for the "old" functions; the case of files using mmap is addressed in a subsequent patch (and there seem to be no problems in this area with files opened with fmemopen). Tested for x86_64.
64 lines
2 KiB
C
64 lines
2 KiB
C
/* Test flushing input file after ungetc (bug 5994).
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Copyright (C) 2025 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library 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 GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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#include <stdio.h>
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#include <support/check.h>
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#include <support/temp_file.h>
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#include <support/xstdio.h>
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#include <support/xunistd.h>
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int
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do_test (void)
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{
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char *filename = NULL;
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int fd = create_temp_file ("tst-ungetc-fflush", &filename);
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TEST_VERIFY_EXIT (fd != -1);
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xclose (fd);
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/* Test as in bug 5994. */
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FILE *fp = xfopen (filename, "w");
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TEST_VERIFY_EXIT (fputs ("#include", fp) >= 0);
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xfclose (fp);
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fp = xfopen (filename, "r");
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TEST_COMPARE (fgetc (fp), '#');
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TEST_COMPARE (fgetc (fp), 'i');
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TEST_COMPARE (ungetc ('@', fp), '@');
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TEST_COMPARE (fflush (fp), 0);
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TEST_COMPARE (lseek (fileno (fp), 0, SEEK_CUR), 1);
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TEST_COMPARE (fgetc (fp), 'i');
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TEST_COMPARE (fgetc (fp), 'n');
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xfclose (fp);
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/* Test as in bug 12799 (duplicate of 5994). */
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fp = xfopen (filename, "w+");
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TEST_VERIFY_EXIT (fputs ("hello world", fp) >= 0);
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rewind (fp);
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TEST_VERIFY (fileno (fp) >= 0);
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char buffer[10];
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TEST_COMPARE (fread (buffer, 1, 5, fp), 5);
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TEST_COMPARE (fgetc (fp), ' ');
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TEST_COMPARE (ungetc ('@', fp), '@');
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TEST_COMPARE (fflush (fp), 0);
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TEST_COMPARE (fgetc (fp), ' ');
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xfclose (fp);
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return 0;
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}
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#include <support/test-driver.c>
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