string/strlcpy.c

   1 /* Copy a null-terminated string to a fixed-size buffer, with length checking.
   2    Copyright (C) 2023-2024 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <https://www.gnu.org/licenses/>.  */
  18
  19 #include <string.h>
  20
  21 size_t
  22 __strlcpy (char *__restrict dest, const char *__restrict src, size_t size)
  23 {
  24   size_t src_length = strlen (src);
  25
  26   if (__glibc_unlikely (src_length >= size))
  27     {
  28       if (size > 0)
  29         {
  30           /* Copy the leading portion of the string.  The last
  31              character is subsequently overwritten with the NUL
  32              terminator, but the destination size is usually a
  33              multiple of a small power of two, so writing it twice
  34              should be more efficient than copying an odd number of
  35              bytes.  */
  36           memcpy (dest, src, size);
  37           dest[size - 1] = '\0';
  38         }
  39     }
  40   else
  41     /* Copy the string and its terminating NUL character.  */
  42     memcpy (dest, src, src_length + 1);
  43   return src_length;
  44 }
  45 libc_hidden_def (__strlcpy)
  46 weak_alias (__strlcpy, strlcpy)