strstr - Man Page

locate a substring


Standard C library (libc, -lc)


#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.

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


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

strstr()Thread safetyMT-Safe
strcasestr()Thread safetyMT-Safe locale


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)

Referenced By

ab(1), index(3), memchr(3), memmem(3), perlapi(1), 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).

2022-10-09 Linux man-pages 6.01