freebsd-dev/lib/libc/string/strcpy.3

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.\"     @(#)strcpy.3	8.1 (Berkeley) 6/4/93
.\" $FreeBSD$
.\"
.Dd June 6, 2018
.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 strcpy
and
.Fn stpcpy
functions
copy the string
.Fa src
to
.Fa dst
(including the terminating
.Ql \e0
character.)
.Pp
The
.Fn strncpy
and
.Fn stpncpy
functions copy at most
.Fa len
characters from
.Fa src
into
.Fa dst .
.Bf Sy
If
.Fa src
is less than
.Fa len
characters long,
the remainder of
.Fa dst
is filled with
.Ql \e0
characters.
.Ef
Otherwise,
.Fa dst
is
.Em not
terminated.
.Pp
For all of
.Fn strcpy ,
.Fn strncpy ,
.Fn stpcpy ,
and
.Fn stpncpy ,
the result is undefined
if
.Fa src
and
.Fa dst
overlap.
.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[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 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 .
.Sh SECURITY CONSIDERATIONS
All of the functions documented in this manual page are easily misused in a
manner which enables malicious users to arbitrarily change a running program's
functionality through a buffer overflow attack.
.Pp
It is strongly suggested that the
.Fn strlcpy
function be used in almost all cases.
.Pp
For some, but not all, fixed-length records, non-terminated strings may be both
valid and desirable.
In that specific case, the
.Fn strncpy
function may be most sensible.