.\"	$OpenBSD: strncat.3,v 1.2 2013/12/19 22:00:58 jmc Exp $
.\"
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.\" This code is derived from software contributed to Berkeley by
.\" Chris Torek and the American National Standards Committee X3,
.\" on Information Processing Systems.
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.Dd $Mdocdate: December 19 2013 $
.Dt STRNCAT 3
.Os
.Sh NAME
.Nm strncat
.Nd concatenate a string with part of another
.Sh SYNOPSIS
.In string.h
.Ft char *
.Fn strncat "char *s" "const char *append" "size_t count"
.Sh DESCRIPTION
The
.Fn strncat
function appends not more than
.Fa count
characters of the NUL-terminated string
.Fa append
to the end of the NUL-terminated string
.Fa s .
Space for the terminating
.Ql \e0
should not be included in
.Fa count .
The string
.Fa s
must have sufficient space to hold the result.
.Sh RETURN VALUES
The
.Fn strncat
function returns the pointer
.Fa s .
.Sh EXAMPLES
The following appends
.Dq Li abc
to
.Va chararray :
.Bd -literal -offset indent
char *letters = "abcdefghi";

(void)strncat(chararray, letters, 3);
.Ed
.Pp
The following example shows how to use
.Fn strncat
safely in conjunction with
.Xr strncpy 3 .
.Bd -literal -offset indent
char buf[BUFSIZ];
char *input, *suffix;

(void)strncpy(buf, input, sizeof(buf) - 1);
buf[sizeof(buf) - 1] = '\e0';
(void)strncat(buf, suffix, sizeof(buf) - 1 - strlen(buf));
.Ed
.Pp
The above will copy as many characters from
.Va input
to
.Va buf
as will fit.
It then appends as many characters from
.Va suffix
as will fit (or none
if there is no space).
For operations like this, the
.Xr strlcpy 3
and
.Xr strlcat 3
functions are a better choice, as shown below.
.Bd -literal -offset indent
(void)strlcpy(buf, input, sizeof(buf));
(void)strlcat(buf, suffix, sizeof(buf));
.Ed
.Sh SEE ALSO
.Xr bcopy 3 ,
.Xr memccpy 3 ,
.Xr memcpy 3 ,
.Xr memmove 3 ,
.Xr strcat 3 ,
.Xr strcpy 3 ,
.Xr strlcpy 3 ,
.Xr wcscat 3 ,
.Xr wcslcpy 3
.Sh STANDARDS
The
.Fn strcat
and
.Fn strncat
functions conform to
.St -ansiC .
.Sh HISTORY
The
.Fn strncat
function first appeared in
.At v7 .