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.\"     @(#)strcpy.3	8.1 (Berkeley) 6/4/93
.\" $FreeBSD: src/lib/libc/string/strcpy.3,v 1.28 2009/04/07 13:42:53 trasz Exp $
.\"
.Dd February 28, 2009
.Dt STRCPY 3
.Os
.Sh NAME
.Nm stpcpy, stpncpy, strcpy , strncpy
.Nd copy strings
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In string.h
.Ft char *
.Fo stpcpy
.Fa "char *s1"
.Fa "const char *s2"
.Fc
.Ft char *
.Fo stpncpy
.Fa "char *restrict s1"
.Fa "const char *restrict s2"
.Fa "size_t n"
.Fc
.Ft char *
.Fo strcpy
.Fa "char *restrict s1"
.Fa "const char *restrict s2"
.Fc
.Ft char *
.Fo strncpy
.Fa "char *restrict s1"
.Fa "const char *restrict s2"
.Fa "size_t n"
.Fc
.Sh DESCRIPTION
The
.Fn stpcpy
and
.Fn strcpy
functions
copy the string
.Fa s2
to
.Fa s1
(including the terminating
.Ql \e0
character).
.Pp
The
.Fn stpncpy
and
.Fn strncpy
functions copy at most
.Fa n
characters from
.Fa s2
into
.Fa s1 .
If
.Fa s2
is less than
.Fa n
characters long,
the remainder of
.Fa s1
is filled with
.Ql \e0
characters.
Otherwise,
.Fa s1
is
.Em not
terminated.
.Pp
The source and destination strings should not overlap, as the
behavior is undefined.
.Sh RETURN VALUES
The
.Fn strcpy
and
.Fn strncpy
functions
return
.Fa s1 .
The
.Fn stpcpy
and
.Fn stpncpy
functions return a pointer to the terminating
.Ql \e0
character of
.Fa s1 .
If
.Fn stpncpy
does not terminate
.Fa s1
with a
.Dv NUL
character, it instead returns a pointer to
.Li s1[n]
(which does not necessarily refer to a valid memory location.)
.Sh EXAMPLES
The following sets
.Va chararray
to
.Dq Li abc\e0\e0\e0 :
.Bd -literal -offset indent
char chararray[6];

(void)strncpy(chararray, "abc", sizeof(chararray));
.Ed
.Pp
The following sets
.Va chararray
to
.Dq Li abcdef :
.Bd -literal -offset indent
char chararray[6];

(void)strncpy(chararray, "abcdefgh", sizeof(chararray));
.Ed
.Pp
Note that it does
.Em not
.Tn NUL
terminate
.Va chararray ,
because the length of the source string is greater than or equal
to the length argument.
.Pp
The following copies as many characters from
.Va input
to
.Va buf
as will fit and
.Tn NUL
terminates the result.
Because
.Fn strncpy
does
.Em not
guarantee to
.Tn NUL
terminate the string itself, this must be done explicitly.
.Bd -literal -offset indent
char buf[1024];

(void)strncpy(buf, input, sizeof(buf) - 1);
buf[sizeof(buf) - 1] = '\e0';
.Ed
.Pp
This could be better achieved using
.Xr strlcpy 3 ,
as shown in the following example:
.Pp
.Dl "(void)strlcpy(buf, input, sizeof(buf));"
.Sh SECURITY CONSIDERATIONS
The
.Fn strcpy ,
.Fn strncpy ,
.Fn stpcpy ,
and
.Fn stpncpy
functions are easily misused in a manner which enables malicious users
to arbitrarily change a running program's functionality through a
buffer overflow attack.
(See
the FSA
and
.Sx EXAMPLES . )
.Pp
It is recommended that
.Xr strlcpy 3
be used instead as a way to avoid such problems.
.Xr strlcpy 3
is not defined in any standards, but it has been adopted by most major libc implementations.
.Sh SEE ALSO
.Xr bcopy 3 ,
.Xr memccpy 3 ,
.Xr memcpy 3 ,
.Xr memmove 3 ,
.Xr strlcpy 3 ,
.Xr wcscpy 3
.Sh STANDARDS
The
.Fn strcpy
and
.Fn strncpy
functions
conform to
.St -isoC .
The
.Fn stpcpy
and
.Fn stpncpy
functions conform to
.St -p1003.1-2008 .
.Sh HISTORY
The
.Fn stpcpy
function first appeared in
.Fx 4.4 ,
and
.Fn stpncpy
was added in
.Fx 8.0 .