'\" 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 strncasecmp 3 2026-08-10 "Linux man-pages 6.19"
.SH NAME
strncasecmp \- nonstrings case-insensitive compare
.SH LIBRARY
Standard C library
.RI ( libc ,\~ \-lc )
.SH SYNOPSIS
.nf
.BR #include\~<strings.h> "  // see memory.h(3head)"
.P
.BI "int strncasecmp(const char " s1 "[], const char " s2 "[], size_t " n );
.fi
.SH DESCRIPTION
The
.BR strncasecmp ()
function is similar to
.BR strcasecmp (3),
except that it compares
no more than
.I n
bytes of
.I s1
and
.IR s2 .
.SH RETURN VALUE
The
.BR strncasecmp ()
function returns
an integer less than, equal to, or greater than zero if
.I s1
is, after ignoring case, found to be
less than, to match, or be greater than
.IR s2 ,
respectively.
.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 strncasecmp ()
T}	Thread safety	MT-Safe locale
.TE
.SH STANDARDS
POSIX.1-2008.
.SH HISTORY
4.4BSD, POSIX.1-2001.
.P
.BR strncasecmp ()
first appeared in 4.4BSD, where it was declared in
.IR <string.h> .
Thus, for reasons of historical compatibility, the glibc
.I <string.h>
header file also declares these functions, if the
.B _DEFAULT_SOURCE
(or, in glibc 2.19 and earlier,
.BR _BSD_SOURCE )
feature test macro is defined.
.P
The POSIX.1-2008 standard says of these functions:
.P
.RS
When the
.B LC_CTYPE
category of the locale being used is from the POSIX locale,
these functions shall behave as if the strings had been converted
to lowercase and then a byte comparison performed.
Otherwise, the results are unspecified.
.RE
.SH SEE ALSO
.BR memory.h (3head),
.BR strncmp (3),
.BR wcsncasecmp (3)