stdio/fgets.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 /* Reads characters from STREAM into S, until either a newline character
  25    is read, N - 1 characters have been read, or EOF is seen.  Returns
  26    the newline, unlike gets.  Finishes by appending a null character and
  27    returning S.  If EOF is seen before any characters have been written
  28    to S, the function returns NULL without appending the null character.
  29    If there is a file error, always return NULL.  */
  30 char *
  31 DEFUN(fgets, (s, n, stream), char *s AND int n AND register FILE *stream)
  32 {
  33   register char *p = s;
  34
  35   if (!__validfp(stream) || s == NULL || n <= 0)
  36     {
  37       errno = EINVAL;
  38       return NULL;
  39     }
  40
  41   if (ferror (stream))
  42     return NULL;
  43
  44   if (stream->__buffer == NULL && stream->__userbuf)
  45     {
  46       /* Unbuffered stream.  Not much optimization to do.  */
  47       register int c = 0;
  48       while (--n > 0 && (c = getc (stream)) != EOF)
  49         if ((*p++ = c) == '\n')
  50           break;
  51       if (c == EOF && (p == s || ferror (stream)))
  52         return NULL;
  53       *p = '\0';
  54       return s;
  55     }
  56
  57   /* Leave space for the null.  */
  58   --n;
  59
  60   if (n > 0 &&
  61       (!stream->__seen || stream->__buffer == NULL || stream->__pushed_back))
  62     {
  63       /* Do one with getc to allocate a buffer.  */
  64       int c = getc (stream);
  65       if (c == EOF)
  66         return NULL;
  67       *p++ = c;
  68       if (c == '\n')
  69         {
  70           *p = '\0';
  71           return s;
  72         }
  73       else
  74         --n;
  75     }
  76
  77   while (n > 0)
  78     {
  79       size_t i;
  80       char *found;
  81
  82       i = stream->__get_limit - stream->__bufp;
  83       if (i == 0)
  84         {
  85           /* Refill the buffer.  */
  86           int c = __fillbf (stream);
  87           if (c == EOF)
  88             break;
  89           *p++ = c;
  90           --n;
  91           if (c == '\n')
  92             {
  93               *p = '\0';
  94               return s;
  95             }
  96           i = stream->__get_limit - stream->__bufp;
  97         }
  98
  99       if (i > n)
 100         i = n;
 101
 102       found = (char *) __memccpy ((PTR) p, stream->__bufp, '\n', i);
 103
 104       if (found != NULL)
 105         {
 106           stream->__bufp += found - p;
 107           p = found;
 108           break;
 109         }
 110
 111       stream->__bufp += i;
 112       n -= i;
 113       p += i;
 114     }
 115
 116   if (p == s)
 117     return NULL;
 118
 119   *p = '\0';
 120   return ferror (stream) ? NULL : s;
 121 }