NetBSD/lib/libc/string/strcpy.3

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.\"     from: @(#)strcpy.3	8.1 (Berkeley) 6/4/93
.\"	$NetBSD: strcpy.3,v 1.19 2009/05/02 09:31:08 wiz Exp $
.\"
.Dd May 1, 2009
.Dt STRCPY 3
.Os
.Sh NAME
.Nm stpcpy ,
.Nm stpncpy ,
.Nm strcpy ,
.Nm strncpy
.Nd copy strings
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In string.h
.Ft char *
.Fn stpcpy "char * restrict dst" "const char * restrict src"
.Ft char *
.Fn stpncpy "char * restrict dst" "const char * restrict src" "size_t len"
.Ft char *
.Fn strcpy "char * restrict dst" "const char * restrict src"
.Ft char *
.Fn strncpy "char * restrict dst" "const char * restrict src" "size_t len"
.Sh DESCRIPTION
The
.Fn stpcpy
and
.Fn strcpy
functions
copy the string
.Fa src
to
.Fa dst
(including the terminating
.Ql \e0
character).
.Pp
The
.Fn stpncpy
and
.Fn strncpy
functions copy at most
.Fa len
characters from
.Fa src
into
.Fa dst .
If
.Fa src
is less than
.Fa len
characters long,
the remainder of
.Fa dst
is filled with
.Ql \e0
characters.
Otherwise,
.Fa dst
is
.Em not
terminated.
.Sh RETURN VALUES
The
.Fn strcpy
and
.Fn strncpy
functions
return
.Fa dst .
The
.Fn stpcpy
and
.Fn stpncpy
functions return a pointer to the terminating
.Ql \e0
character of
.Fa dst .
If
.Fn stpncpy
does not terminate
.Fa dst
with a
.Dv NUL
character, it instead returns a pointer to
.Li dst[len]
(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 parameter.
.Fn strncpy
.Em only
.Tn NUL
terminates
the destination string when the length of the source
string is less than the length parameter.
.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 and more simply achieved using
.Xr strlcpy 3 ,
as shown in the following example:
.Bd -literal -offset indent
(void)strlcpy(buf, input, sizeof(buf));
.Ed
.Pp
Note that because
.Xr strlcpy 3
is not defined in any standards, it should
only be used when portability is not a concern.
.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-99 .
The
.Fn stpcpy
and
.Fn stpncpy
functions conform to
.St -p1003.1-2008 .
.Sh HISTORY
The
.Fn stpcpy
and
.Fn stpncpy
functions first appeared in
.Nx 6.0 .
.Sh SECURITY CONSIDERATIONS
The
.Fn strcpy
and
.Fn stpcpy
functions are easily misused in a manner which enables malicious users
to arbitrarily change a running program's functionality through a
buffer overflow attack.