stdio/fread.c

   1 /* Copyright (C) 1991, 1992, 1995 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 Library General Public License as
   6 published by the Free Software Foundation; either version 2 of the
   7 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 Library General Public License for more details.
  13
  14 You should have received a copy of the GNU Library General Public
  15 License along with the GNU C Library; see the file COPYING.LIB.  If
  16 not, write to the Free Software Foundation, Inc., 675 Mass Ave,
  17 Cambridge, MA 02139, USA.  */
  18
  19 #include <ansidecl.h>
  20 #include <errno.h>
  21 #include <stdio.h>
  22 #include <string.h>
  23
  24
  25 #define default_func    __default_room_functions.__input
  26
  27 /* Read NMEMB chunks of SIZE bytes each from STREAM into P.  */
  28 size_t
  29 DEFUN(fread, (p, size, nmemb, stream),
  30       PTR p AND size_t size AND size_t nmemb AND register FILE *stream)
  31 {
  32   register char *ptr = (char *) p;
  33   register size_t to_read = size * nmemb;
  34   size_t bytes = to_read;
  35
  36   if (!__validfp(stream) || !stream->__mode.__read)
  37     {
  38       errno = EINVAL;
  39       return 0;
  40     }
  41   if (feof(stream) || ferror(stream))
  42     return 0;
  43   if (p == NULL || to_read == 0)
  44     return 0;
  45
  46   if (!stream->__seen || stream->__buffer == NULL || stream->__pushed_back)
  47     {
  48       /* This stream has never been seen before, or it has a character
  49          pushed back.  Call __fillbf to deal with those cases.  Life will
  50          be simpler after this call.  */
  51       int c = __fillbf(stream);
  52       if (c == EOF)
  53         return 0;
  54       *ptr++ = c;
  55       if (--to_read == 0)
  56         return 1;
  57     }
  58
  59  read_from_buffer:;
  60   if (stream->__bufp < stream->__get_limit)
  61     {
  62       /* First off, empty out the buffer.  */
  63       register size_t copy = stream->__get_limit - stream->__bufp;
  64       if (copy > to_read)
  65         copy = to_read;
  66       to_read -= copy;
  67       if (copy > 20)
  68         memcpy((PTR) ptr, (PTR) stream->__bufp, copy);
  69       else
  70         {
  71           register size_t i;
  72           for (i = 0; i < copy; ++i)
  73             ptr[i] = stream->__bufp[i];
  74         }
  75       stream->__bufp += copy;
  76       if (to_read == 0)
  77         return nmemb;
  78       ptr += copy;
  79     }
  80
  81   /* Reading directly into the user's buffer doesn't help when
  82      using a user-specified input buffer filling/expanding function,
  83      so we don't do it in that case.  */
  84   if (to_read >= stream->__bufsize &&
  85       stream->__room_funcs.__input == default_func &&
  86       stream->__offset == stream->__target)
  87     {
  88       /* Read directly into the user's buffer.  */
  89       if (stream->__io_funcs.__read != NULL)
  90         while (to_read > 0)
  91           {
  92             register int count;
  93             count = (*stream->__io_funcs.__read)(stream->__cookie,
  94                                                  ptr, to_read);
  95             if (count > 0)
  96               {
  97                 to_read -= count;
  98                 if (stream->__offset != -1)
  99                   {
 100                     stream->__offset += count;
 101                     stream->__target += count;
 102                   }
 103                 ptr += count;
 104               }
 105             else if (count == 0)
 106               {
 107                 stream->__eof = 1;
 108                 break;
 109               }
 110             else
 111               {
 112                 stream->__error = 1;
 113                 break;
 114               }
 115           }
 116       else
 117         stream->__eof = 1;
 118     }
 119   else
 120     {
 121       int c = __fillbf(stream);
 122       if (c == EOF)
 123         return (bytes - to_read) / size;
 124       *ptr++ = (char) c;
 125       --to_read;
 126       if (to_read > 0)
 127         goto read_from_buffer;
 128     }
 129
 130   return (bytes - to_read) / size;
 131 }