strstr, strcasestr - locate a substring


strcasestr - locate a substring

Header Files

#include <cs50.h>
#define _GNU_SOURCE


string strcasestr(string haystack, string needle);

Defining _GNU_SOURCE in this way enables strcasestr within string.h.

#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);


This function searches haystack for (the first occurrence of) needle case-insensitively. In other words, it determines whether (and where) needle is a substring of haystack, ignoring case.

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.


If needle is found in haystack, ignoring case, this function returns the substring of haystack that begins with needle. (For instance, if haystack is "FOO BAR BAR BAZ" and needle is "bar", this function returns "BAR BAR BAZ".) If needle is not found in haystack, ignoring case, this function returns NULL.

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


#include <cs50.h>
#define _GNU_SOURCE
int main(void) { string haystack = "FOO BAR BAR BAZ"; string needle = "bar"; string match = strstr(haystack, needle); if (match) { printf("%s\n", match); } }


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


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

The strcasestr() function is a nonstandard extension.


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


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