'\" t
.\" Copyright 1993, David Metcalfe <david@prism.demon.co.uk>
.\" Copyright, the authors of the Linux man-pages project
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.TH strcasestr 3 2026-05-16 "Linux man-pages 6.19"
.SH NAME
strcasestr \- string case-insensitive search substring
.SH LIBRARY
Standard C library
.RI ( libc ,\~ \-lc )
.SH SYNOPSIS
.nf
.BR #define\~_GNU_SOURCE "  // See feature_test_macros(7)"
.B #include <string.h>
.P
.BI "char *strcasestr(const char *" haystack ", const char *" needle );
.fi
.SH DESCRIPTION
.BR strcasestr ()
is like
.BR strstr (),
but ignores the case of both arguments.
.SH RETURN VALUE
See
.BR strstr (3).
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.TS
allbox;
lbx lb lb
l l l.
Interface	Attribute	Value
T{
.na
.nh
.BR strcasestr ()
T}	Thread safety	MT-Safe locale
.TE
.SH STANDARDS
GNU.
.SH HISTORY
GNU.
.SH SEE ALSO
.BR string (3),
.BR strstr (3)