strcasestr(3) Library Functions Manual strcasestr(3)

strcasestr - string case-insensitive search substring

Standard C library (libc-lc)

#define _GNU_SOURCE  // See feature_test_macros(7)
#include <string.h>
char *strcasestr(const char *haystack, const char *needle);

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

See strstr(3).

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

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

GNU.

GNU.

string(3), strstr(3)

2026-05-16 Linux man-pages 6.19