stdio/fread.c

   1 /* Copyright (C) 1991, 1992, 1995, 1996, 1997 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 not,
  16    write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  17    Boston, MA 02111-1307, USA.  */
  18
  19 #include <errno.h>
  20 #include <stdio.h>
  21 #include <string.h>
  22
  23
  24 #define default_func    __default_room_functions.__input
  25
  26 /* Read NMEMB chunks of SIZE bytes each from STREAM into P.  */
  27 size_t
  28 fread (p, size, nmemb, stream)
  29      void *p;
  30      size_t size;
  31      size_t nmemb;
  32      register FILE *stream;
  33 {
  34   register char *ptr = (char *) p;
  35   register size_t to_read = size * nmemb;
  36   size_t bytes = to_read;
  37
  38   if (!__validfp (stream) || !stream->__mode.__read)
  39     {
  40       __set_errno (EINVAL);
  41       return 0;
  42     }
  43   if (feof (stream) || ferror (stream))
  44     return 0;
  45   if (p == NULL || to_read == 0)
  46     return 0;
  47
  48   if (!stream->__seen || stream->__buffer == NULL || stream->__pushed_back)
  49     {
  50       /* This stream has never been seen before, or it has a character
  51          pushed back.  Call __fillbf to deal with those cases.  Life will
  52          be simpler after this call.  */
  53       int c = __fillbf (stream);
  54       if (c == EOF)
  55         return 0;
  56       *ptr++ = c;
  57       if (--to_read == 0)
  58         return 1;
  59     }
  60
  61  read_from_buffer:;
  62   if (stream->__bufp < stream->__get_limit)
  63     {
  64       /* First off, empty out the buffer.  */
  65       register size_t copy = stream->__get_limit - stream->__bufp;
  66       if (copy > to_read)
  67         copy = to_read;
  68       to_read -= copy;
  69       if (copy > 20)
  70         memcpy((void *) ptr, (void *) stream->__bufp, copy);
  71       else
  72         {
  73           register size_t i;
  74           for (i = 0; i < copy; ++i)
  75             ptr[i] = stream->__bufp[i];
  76         }
  77       stream->__bufp += copy;
  78       if (to_read == 0)
  79         return nmemb;
  80       ptr += copy;
  81     }
  82
  83   /* Reading directly into the user's buffer doesn't help when
  84      using a user-specified input buffer filling/expanding function,
  85      so we don't do it in that case.  */
  86   if (to_read >= stream->__bufsize &&
  87       stream->__room_funcs.__input == default_func &&
  88       stream->__offset == stream->__target)
  89     {
  90       /* Read directly into the user's buffer.  */
  91       if (stream->__io_funcs.__read != NULL)
  92         while (to_read > 0)
  93           {
  94             register int count;
  95             count = (*stream->__io_funcs.__read) (stream->__cookie,
  96                                                   ptr, to_read);
  97             if (count > 0)
  98               {
  99                 to_read -= count;
 100                 if (stream->__offset != -1)
 101                   {
 102                     stream->__offset += count;
 103                     stream->__target += count;
 104                   }
 105                 ptr += count;
 106               }
 107             else if (count == 0)
 108               {
 109                 stream->__eof = 1;
 110                 break;
 111               }
 112             else
 113               {
 114                 stream->__error = 1;
 115                 break;
 116               }
 117           }
 118       else
 119         stream->__eof = 1;
 120     }
 121   else
 122     {
 123       int c = __fillbf (stream);
 124       if (c == EOF)
 125         return (bytes - to_read) / size;
 126       *ptr++ = (char) c;
 127       --to_read;
 128       if (to_read > 0)
 129         goto read_from_buffer;
 130     }
 131
 132   return (bytes - to_read) / size;
 133 }