strstr(3)		    Library Functions Manual		       strstr(3)

NAME
     strstr, strcasestr - locate a substring

LIBRARY
     Standard C library (libc, -lc)

SYNOPSIS
     #include <string.h>

     char *strstr(const char *haystack, const char *needle);

     #define _GNU_SOURCE	 /* See feature_test_macros(7) */
     #include <string.h>

     char *strcasestr(const char *haystack, const char *needle);

DESCRIPTION
     The strstr() function finds the first occurrence of the substring needle in
     the string haystack.  The terminating null bytes ('\0') are not compared.

     It is equivalent to

	 memmem(haystack, strlen(haystack), needle, strlen(needle))

     The  strcasestr()	function  is like strstr(), but ignores the case of both
     arguments.

RETURN VALUE
     These functions return a pointer to the beginning of the located substring,
     or NULL if the substring is not found.

     If needle is the empty string, the return value is always haystack itself.

ATTRIBUTES
     For an explanation of the terms used in this  section,  see  attributes(7).
     allbox; lbx lb lb l l l.  Interface Attribute Value T{ strstr() T}	  Thread
     safety  MT-Safe T{ strcasestr() T}	  Thread safety	 MT-Safe locale

STANDARDS
     strstr()
	    C11, POSIX.1-2008.

     strcasestr()
	    GNU.

HISTORY
     strstr()
	    POSIX.1-2001, C89.

     strcasestr()
	    GNU.

SEE ALSO
     memchr(3),	 memmem(3),  strcasecmp(3),  strchr(3),	 string(3),  strpbrk(3),
     strsep(3), strspn(3), strtok(3), wcsstr(3)

Linux man-pages 6.18		   2026-02-25			       strstr(3)