stdio/fgets.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 /* Reads characters from STREAM into S, until either a newline character
  24    is read, N - 1 characters have been read, or EOF is seen.  Returns
  25    the newline, unlike gets.  Finishes by appending a null character and
  26    returning S.  If EOF is seen before any characters have been written
  27    to S, the function returns NULL without appending the null character.
  28    If there is a file error, always return NULL.  */
  29 char *
  30 fgets (s, n, stream)
  31      char *s;
  32      int n;
  33      register FILE *stream;
  34 {
  35   register char *p = s;
  36
  37   if (!__validfp (stream) || s == NULL || n <= 0)
  38     {
  39       __set_errno (EINVAL);
  40       return NULL;
  41     }
  42
  43   if (ferror (stream))
  44     return NULL;
  45
  46   if (stream->__buffer == NULL && stream->__userbuf)
  47     {
  48       /* Unbuffered stream.  Not much optimization to do.  */
  49       register int c = 0;
  50       while (--n > 0 && (c = getc (stream)) != EOF)
  51         if ((*p++ = c) == '\n')
  52           break;
  53       if (c == EOF && (p == s || ferror (stream)))
  54         return NULL;
  55       *p = '\0';
  56       return s;
  57     }
  58
  59   /* Leave space for the null.  */
  60   --n;
  61
  62   if (n > 0 &&
  63       (!stream->__seen || stream->__buffer == NULL || stream->__pushed_back))
  64     {
  65       /* Do one with getc to allocate a buffer.  */
  66       int c = getc (stream);
  67       if (c == EOF)
  68         return NULL;
  69       *p++ = c;
  70       if (c == '\n')
  71         {
  72           *p = '\0';
  73           return s;
  74         }
  75       else
  76         --n;
  77     }
  78
  79   while (n > 0)
  80     {
  81       size_t i;
  82       char *found;
  83
  84       i = stream->__get_limit - stream->__bufp;
  85       if (i == 0)
  86         {
  87           /* Refill the buffer.  */
  88           int c = __fillbf (stream);
  89           if (c == EOF)
  90             break;
  91           *p++ = c;
  92           --n;
  93           if (c == '\n')
  94             {
  95               *p = '\0';
  96               return s;
  97             }
  98           i = stream->__get_limit - stream->__bufp;
  99         }
 100
 101       if (i > n)
 102         i = n;
 103
 104       found = (char *) __memccpy ((void *) p, stream->__bufp, '\n', i);
 105
 106       if (found != NULL)
 107         {
 108           stream->__bufp += found - p;
 109           p = found;
 110           break;
 111         }
 112
 113       stream->__bufp += i;
 114       n -= i;
 115       p += i;
 116     }
 117
 118   if (p == s)
 119     return NULL;
 120
 121   *p = '\0';
 122   return ferror (stream) ? NULL : s;
 123 }