newlib/libc/string/strnstr.c

   1 /*
   2 FUNCTION
   3         <<strnstr>>---find string segment
   4
   5 INDEX
   6         strnstr
   7
   8 SYNOPSIS
   9         #include <string.h>
  10         size_t strnstr(const char *<[s1]>, const char *<[s2]>, size_t <[n]>);
  11
  12 DESCRIPTION
  13         Locates the first occurrence in the string pointed to by <[s1]> of
  14         the sequence of limited to the <[n]> characters in the string
  15         pointed to by <[s2]>
  16
  17 RETURNS
  18         Returns a pointer to the located string segment, or a null
  19         pointer if the string <[s2]> is not found. If <[s2]> points to
  20         a string with zero length, <[s1]> is returned.
  21
  22
  23 PORTABILITY
  24 <<strnstr>> is a BSD extension.
  25
  26 <<strnstr>> requires no supporting OS subroutines.
  27
  28 QUICKREF
  29         strnstr pure
  30
  31 */
  32
  33 #define _GNU_SOURCE
  34 #include <string.h>
  35
  36 /*
  37  * Find the first occurrence of find in s, where the search is limited to the
  38  * first slen characters of s.
  39  */
  40 char *
  41 strnstr(const char *haystack, const char *needle, size_t haystack_len)
  42 {
  43   size_t needle_len = strnlen(needle, haystack_len);
  44
  45   if (needle_len < haystack_len || !needle[needle_len]) {
  46     char *x = memmem(haystack, haystack_len, needle, needle_len);
  47     if (x && !memchr(haystack, 0, x - haystack))
  48       return x;
  49   }
  50   return NULL;
  51 }