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strstr(3) — Linux manual page

strstr(3)                Library Functions Manualstrstr(3)

NAME        top

       strstr, strcasestr - locate a substring

LIBRARY        top

       Standard C library (libc,-lc)

SYNOPSIS        top

#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        top

       Thestrstr() function finds the first occurrence of the substringneedle in the stringhaystack.  The terminating null bytes ('\0')       are not compared.       Thestrcasestr() function is likestrstr(), but ignores the case       of both arguments.

RETURN VALUE        top

       These functions return a pointer to the beginning of the located       substring, or NULL if the substring is not found.       Ifneedle is the empty string, the return value is alwayshaystack       itself.

ATTRIBUTES        top

       For an explanation of the terms used in this section, seeattributes(7).       ┌───────────────────────────────┬───────────────┬────────────────┐       │Interface│Attribute│Value│       ├───────────────────────────────┼───────────────┼────────────────┤       │strstr()                      │ Thread safety │ MT-Safe        │       ├───────────────────────────────┼───────────────┼────────────────┤       │strcasestr()                  │ Thread safety │ MT-Safe locale │       └───────────────────────────────┴───────────────┴────────────────┘

STANDARDS        top

strstr()              C11, POSIX.1-2008.strcasestr()              GNU.

HISTORY        top

strstr()              POSIX.1-2001, C89.strcasestr()              GNU.

SEE ALSO        top

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

COLOPHON        top

       This page is part of theman-pages (Linux kernel and C library       user-space interface documentation) project.  Information about       the project can be found at        ⟨https://www.kernel.org/doc/man-pages/⟩.  If you have a bug report       for this manual page, see       ⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.       This page was obtained from the tarball man-pages-6.15.tar.gz       fetched from       ⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on       2025-08-11.  If you discover any rendering problems in this HTML       version of the page, or you believe there is a better or more up-       to-date source for the page, or you have corrections or       improvements to the information in this COLOPHON (which isnot       part of the original manual page), send a mail to       man-pages@man7.orgLinux man-pages 6.15            2025-05-17strstr(3)

Pages that refer to this page:memchr(3), memmem(3), strchr(3), string(3), strpbrk(3), strsep(3), strspn(3), strtok(3), wcsstr(3), signal-safety(7)

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