libio/iofgets.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 #include <stdio.h>
  29
  30 char *
  31 _IO_fgets (char *buf, int n, FILE *fp)
  32 {
  33   size_t count;
  34   char *result;
  35   int old_error;
  36   CHECK_FILE (fp, NULL);
  37   if (n <= 0)
  38     return NULL;
  39   if (__glibc_unlikely (n == 1))
  40     {
  41       /* Another irregular case: since we have to store a NUL byte and
  42          there is only room for exactly one byte, we don't have to
  43          read anything.  */
  44       buf[0] = '\0';
  45       return buf;
  46     }
  47   _IO_acquire_lock (fp);
  48   /* This is very tricky since a file descriptor may be in the
  49      non-blocking mode. The error flag doesn't mean much in this
  50      case. We return an error only when there is a new error. */
  51   old_error = fp->_flags & _IO_ERR_SEEN;
  52   fp->_flags &= ~_IO_ERR_SEEN;
  53   count = _IO_getline (fp, buf, n - 1, '\n', 1);
  54   /* If we read in some bytes and errno is EAGAIN, that error will
  55      be reported for next read. */
  56   if (count == 0 || ((fp->_flags & _IO_ERR_SEEN) && errno != EAGAIN))
  57     result = NULL;
  58   else
  59     {
  60       buf[count] = '\0';
  61       result = buf;
  62     }
  63   fp->_flags |= old_error;
  64   _IO_release_lock (fp);
  65   return result;
  66 }
  67
  68 weak_alias (_IO_fgets, fgets)
  69
  70 # ifndef _IO_MTSAFE_IO
  71 strong_alias (_IO_fgets, __fgets_unlocked)
  72 libc_hidden_def (__fgets_unlocked)
  73 weak_alias (_IO_fgets, fgets_unlocked)
  74 libc_hidden_weak (fgets_unlocked)
  75 # endif