nuttx/libs/libc/string/lib_strstr.c

/****************************************************************************
 * libs/libc/string/lib_strstr.c
 *
 *   Copyright (C) 2009, 2011 Gregory Nutt. All rights reserved.
 *   Author: Gregory Nutt <gnutt@nuttx.org>
 *
 * Redistribution and use str source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions str binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer str
 *    the documentation and/or other materials provided with the
 *    distribution.
 * 3. Neither the name NuttX nor the names of its contributors may be
 *    used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 *
 ****************************************************************************/

/****************************************************************************
 * Included Files
 ****************************************************************************/

#include <nuttx/config.h>

#include <string.h>

/****************************************************************************
 * Public Functions
 ****************************************************************************/

FAR char *strstr(FAR const char *str, FAR const char *substr)
{
  FAR const char *candidate; /* Candidate in str with matching start character */
  char ch;                   /* First character of the substring */
  size_t len;                /* The length of the substring */

  /* Special case the empty substring */

  len = strlen(substr);
  ch  = *substr;

  if (!ch)
    {
      /* We'll say that an empty substring matches at the beginning of
       * the string
       */

      return (FAR char *)str;
    }

  /* Search for the substring */

  candidate = str;
  for (; ; )
    {
      /* strchr() will return a pointer to the next occurrence of the
       * character ch in the string
       */

      candidate = strchr(candidate, ch);
      if (!candidate || strlen(candidate) < len)
        {
          /* First character of the substring does not appear in the string
           * or the remainder of the string is not long enough to contain the
           * substring.
           */

          return NULL;
        }

      /* Check if this is the beginning of a matching substring */

      if (strncmp(candidate, substr, len) == 0)
        {
          return (FAR char *)candidate;
        }

      /* No, find the next candidate after this one */

      candidate++;
    }

  /* Won't get here, but some compilers might complain.  Other compilers
   * might complain about this code being unreachable too.
   */

  return NULL;
}