libio/iosetvbuf.c

   1 /* Copyright (C) 1993-2023 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the License, or (at your option) any later version.
   8
   9    The GNU C Library 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 GNU
  12    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, see
  16    <https://www.gnu.org/licenses/>.
  17
  18    As a special exception, if you link the code in this file with
  19    files compiled with a GNU compiler to produce an executable,
  20    that does not cause the resulting executable to be covered by
  21    the GNU Lesser General Public License.  This exception does not
  22    however invalidate any other reasons why the executable file
  23    might be covered by the GNU Lesser General Public License.
  24    This exception applies to code released by its copyright holders
  25    in files containing the exception.  */
  26
  27 #include "libioP.h"
  28
  29 #define _IOFBF 0 /* Fully buffered. */
  30 #define _IOLBF 1 /* Line buffered. */
  31 #define _IONBF 2 /* No buffering. */
  32
  33 int
  34 _IO_setvbuf (FILE *fp, char *buf, int mode, size_t size)
  35 {
  36   int result;
  37   CHECK_FILE (fp, EOF);
  38   _IO_acquire_lock (fp);
  39   switch (mode)
  40     {
  41     case _IOFBF:
  42       fp->_flags &= ~(_IO_LINE_BUF|_IO_UNBUFFERED);
  43       if (buf == NULL)
  44         {
  45           if (fp->_IO_buf_base == NULL)
  46             {
  47               /* There is no flag to distinguish between "fully buffered
  48                  mode has been explicitly set" as opposed to "line
  49                  buffering has not been explicitly set".  In both
  50                  cases, _IO_LINE_BUF is off.  If this is a tty, and
  51                  _IO_filedoalloc later gets called, it cannot know if
  52                  it should set the _IO_LINE_BUF flag (because that is
  53                  the default), or not (because we have explicitly asked
  54                  for fully buffered mode).  So we make sure a buffer
  55                  gets allocated now, and explicitly turn off line
  56                  buffering.
  57
  58                  A possibly cleaner alternative would be to add an
  59                  extra flag, but then flags are a finite resource.  */
  60               if (_IO_DOALLOCATE (fp) < 0)
  61                 {
  62                   result = EOF;
  63                   goto unlock_return;
  64                 }
  65               fp->_flags &= ~_IO_LINE_BUF;
  66             }
  67           result = 0;
  68           goto unlock_return;
  69         }
  70       break;
  71     case _IOLBF:
  72       fp->_flags &= ~_IO_UNBUFFERED;
  73       fp->_flags |= _IO_LINE_BUF;
  74       if (buf == NULL)
  75         {
  76           result = 0;
  77           goto unlock_return;
  78         }
  79       break;
  80     case _IONBF:
  81       fp->_flags &= ~_IO_LINE_BUF;
  82       fp->_flags |= _IO_UNBUFFERED;
  83       buf = NULL;
  84       size = 0;
  85       break;
  86     default:
  87       result = EOF;
  88       goto unlock_return;
  89     }
  90   result = _IO_SETBUF (fp, buf, size) == NULL ? EOF : 0;
  91
  92 unlock_return:
  93   _IO_release_lock (fp);
  94   return result;
  95 }
  96 libc_hidden_def (_IO_setvbuf)
  97
  98 weak_alias (_IO_setvbuf, setvbuf)