libc/src/stdio/fgets.cpp

   1 //===-- Implementation of fgets -------------------------------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #include "src/stdio/fgets.h"
  10 #include "src/__support/File/file.h"
  11
  12 #include <errno.h>
  13 #include <stddef.h>
  14 #include <stdio.h>
  15
  16 namespace __llvm_libc {
  17
  18 LLVM_LIBC_FUNCTION(char *, fgets,
  19                    (char *__restrict str, int count,
  20                     ::FILE *__restrict raw_stream)) {
  21   if (count < 1)
  22     return nullptr;
  23
  24   unsigned char c = '\0';
  25   auto stream = reinterpret_cast<__llvm_libc::File *__restrict>(raw_stream);
  26   stream->lock();
  27
  28   // i is an int because it's frequently compared to count, which is also int.
  29   int i = 0;
  30
  31   for (; i < (count - 1) && c != '\n'; ++i) {
  32     auto result = stream->read_unlocked(&c, 1);
  33     size_t r = result.value;
  34     if (result.has_error())
  35       errno = result.error;
  36
  37     if (r != 1)
  38       break;
  39     str[i] = c;
  40   }
  41
  42   bool has_error = stream->error_unlocked();
  43   bool has_eof = stream->iseof_unlocked();
  44   stream->unlock();
  45
  46   // If the requested read size makes no sense, an error occured, or no bytes
  47   // were read due to an EOF, then return nullptr and don't write the null byte.
  48   if (has_error || (i == 0 && has_eof))
  49     return nullptr;
  50
  51   str[i] = '\0';
  52   return str;
  53 }
  54
  55 } // namespace __llvm_libc