string/strncat.c

   1 /*
   2  * Copyright (c) 2011 Apple, Inc. All rights reserved.
   3  *
   4  * @APPLE_LICENSE_HEADER_START@
   5  *
   6  * This file contains Original Code and/or Modifications of Original Code
   7  * as defined in and that are subject to the Apple Public Source License
   8  * Version 2.0 (the 'License'). You may not use this file except in
   9  * compliance with the License. Please obtain a copy of the License at
  10  * http://www.opensource.apple.com/apsl/ and read it before using this
  11  * file.
  12  *
  13  * The Original Code and all software distributed under the License are
  14  * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
  15  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
  16  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
  17  * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
  18  * Please see the License for the specific language governing rights and
  19  * limitations under the License.
  20  *
  21  * @APPLE_LICENSE_HEADER_END@
  22  */
  23
  24 #include <string.h>
  25
  26 char *
  27 strncat(char *restrict dst, const char *restrict src, size_t maxlen) {
  28         const size_t dstlen = strlen(dst);
  29         const size_t srclen = strnlen(src, maxlen);
  30     //  The strcat() and strncat() functions append a copy of the null-
  31     //  terminated string src to the end of the null-terminated string dst,
  32     //  then add a terminating '\0'.  The string dst must have sufficient
  33     //  space to hold the result.
  34     //
  35     //  The strncat() function appends not more than maxlen characters
  36     //  from src, and then adds a terminating '\0'.
  37     const size_t cpylen = srclen < maxlen ? srclen : maxlen;
  38     memcpy(dst+dstlen, src, cpylen);
  39     dst[dstlen+cpylen] = '\0';
  40     //  The strcat() and strncat() functions return dst.
  41     return dst;
  42 }