File: strstr.c

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/* Simple implementation of strstr for systems without it.
   This function is in the public domain.  */

/*

@deftypefn Supplemental char* strstr (const char *@var{string}, const char *@var{sub})

This function searches for the substring @var{sub} in the string
@var{string}, not including the terminating null characters.  A pointer
to the first occurrence of @var{sub} is returned, or @code{NULL} if the
substring is absent.  If @var{sub} points to a string with zero
length, the function returns @var{string}.

@end deftypefn


*/

#include <stddef.h>

extern char *strchr (const char *, int);
extern int strncmp (const void *, const void *, size_t);
extern size_t strlen (const char *);

char *
strstr (const char *s1, const char *s2)
{
  const char *p = s1;
  const size_t len = strlen (s2);

  if (!len)
    return s1;

  for (; (p = strchr (p, *s2)) != 0; p++)
    {
      if (strncmp (p, s2, len) == 0)
	return (char *)p;
    }
  return (0);
}