1  /* Test of POSIX compatible fflush() function.
       2     Copyright (C) 2008-2022 Free Software Foundation, Inc.
       3  
       4     This program is free software: you can redistribute it and/or modify
       5     it under the terms of the GNU General Public License as published by
       6     the Free Software Foundation, either version 3 of the License, or
       7     (at your option) any later version.
       8  
       9     This program is distributed in the hope that it will be useful,
      10     but WITHOUT ANY WARRANTY; without even the implied warranty of
      11     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
      12     GNU General Public License for more details.
      13  
      14     You should have received a copy of the GNU General Public License
      15     along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
      16  
      17  #include <config.h>
      18  
      19  #include <stdio.h>
      20  
      21  #include "binary-io.h"
      22  #include "macros.h"
      23  
      24  int
      25  main (int argc, char **argv)
      26  {
      27    int c;
      28  
      29    /* Avoid the well-known bugs of fflush() on streams in O_TEXT mode
      30       on native Windows platforms.  */
      31    set_binary_mode (0, O_BINARY);
      32  
      33    if (argc > 1)
      34      switch (argv[1][0])
      35        {
      36        case '1':
      37          /* Check fflush after a backup ungetc() call.  This is case 1a in
      38             terms of
      39             <https://lists.gnu.org/r/bug-gnulib/2008-03/msg00131.html>,
      40             according to the Austin Group's resolution on 2009-01-08.  */
      41  
      42          c = fgetc (stdin);
      43          ASSERT (c == '#');
      44  
      45          c = fgetc (stdin);
      46          ASSERT (c == '!');
      47  
      48          /* Here the file-position indicator must be 2.  */
      49  
      50          c = ungetc ('!', stdin);
      51          ASSERT (c == '!');
      52  
      53          fflush (stdin);
      54  
      55          /* Here the file-position indicator must be 1.  */
      56  
      57          c = fgetc (stdin);
      58          ASSERT (c == '!');
      59  
      60          c = fgetc (stdin);
      61          ASSERT (c == '/');
      62  
      63          return 0;
      64  
      65        case '2':
      66          /* Check fflush after a non-backup ungetc() call.  This is case 2a in
      67             terms of
      68             <https://lists.gnu.org/r/bug-gnulib/2008-03/msg00131.html>,
      69             according to the Austin Group's resolution on 2009-01-08.  */
      70          /* Check that fflush after a non-backup ungetc() call discards the
      71             ungetc buffer.  This is mandated by POSIX
      72             <https://pubs.opengroup.org/onlinepubs/9699919799/functions/fflush.html>:
      73               "...any characters pushed back onto the stream by ungetc()
      74                or ungetwc() that have not subsequently been read from the
      75                stream shall be discarded..."  */
      76  
      77          c = fgetc (stdin);
      78          ASSERT (c == '#');
      79  
      80          c = fgetc (stdin);
      81          ASSERT (c == '!');
      82  
      83          /* Here the file-position indicator must be 2.  */
      84  
      85          c = ungetc ('@', stdin);
      86          ASSERT (c == '@');
      87  
      88          fflush (stdin);
      89  
      90          /* Here the file-position indicator must be 1.  */
      91  
      92          c = fgetc (stdin);
      93          ASSERT (c == '!');
      94  
      95          c = fgetc (stdin);
      96          ASSERT (c == '/');
      97  
      98          return 0;
      99        }
     100  
     101    return 1;
     102  }