strstr(3)                  Library Functions Manual                  strstr(3)

NAME
       strstr - string search substring

LIBRARY
       Standard C library (libc, -lc)

SYNOPSIS
       #include <string.h>

       char *strstr(const char *haystack, const char *needle);

DESCRIPTION
       strstr() finds the first occurrence of the substring needle in the
       string haystack.

       The terminating null bytes ('\0') are not compared.

       It is equivalent to

           memmem(haystack, strlen(haystack), needle, strlen(needle))

RETURN VALUE
       strstr(3) returns 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.

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

       +--------------------------------------------+---------------+---------+
       |Interface                                   | Attribute     | Value   |
       +--------------------------------------------+---------------+---------+
       |strstr ()                                   | Thread safety | MT-Safe |
       +--------------------------------------------+---------------+---------+
STANDARDS
       C11, POSIX.1-2008.

HISTORY
       POSIX.1-2001, C89.

SEE ALSO
       strcasestr(3), strchr(3), string(3), strpbrk(3), strsep(3), strspn(3),
       wcsstr(3)

Linux man-pages 6.19              2026-08-10                         strstr(3)