strstr, strcasestr — locate a substring


#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);


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

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.


For an explanation of the terms used in this section, see attributes(7).

Interface Attribute Value
strstr() Thread safety MT-Safe
strcasestr() Thread safety MT-Safe locale

Conforming to

strstr(): POSIX.1-2001, POSIX.1-2008, C89, C99.

The strcasestr() function is a nonstandard extension.

See Also

index(3), memchr(3), memmem(3), rindex(3), strcasecmp(3), strchr(3), string(3), strpbrk(3), strsep(3), strspn(3), strtok(3), wcsstr(3)


This page is part of release 5.04 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at

Referenced By

ab(1), index(3), memchr(3), memmem(3), signal-safety(7), strchr(3), string(3), strnstr.3bsd(3), strpbrk(3), strsep(3), strspn(3), strtok(3), wcsstr(3).

The man page strcasestr(3) is an alias of strstr(3).

2019-03-06 GNU Linux Programmer's Manual