Libc-583.tar.gz

[apple/libc.git] / string / strcpy.3

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.\"     @(#)strcpy.3	8.1 (Berkeley) 6/4/93
.\" $FreeBSD: src/lib/libc/string/strcpy.3,v 1.24 2002/12/19 09:40:24 ru Exp $
.\"
.Dd August 9, 2001
.Dt STRCPY 3
.Os
.Sh NAME
.Nm stpcpy ,
.Nm strcpy ,
.Nm 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 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 strncpy
function copies 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
function returns a pointer to the terminating
.Ql \e0
character of
.Fa s1 .
.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));"
.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 SECURITY CONSIDERATIONS
The
.Fn strcpy
function is 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 . )
.Sh SEE ALSO
.Xr bcopy 3 ,
.Xr memccpy 3 ,
.Xr memcpy 3 ,
.Xr memmove 3 ,
.Xr strlcpy 3
.Sh STANDARDS
The
.Fn strcpy
and
.Fn strncpy
functions
conform to
.St -isoC .
The
.Fn stpcpy
function is an MS-DOS and GNUism.
The
.Fn stpcpy
function
conforms to no standard.
.Sh HISTORY
The
.Fn stpcpy
function first appeared in
.Fx 4.4 ,
coming from 1998-vintage Linux.