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.Dd $Mdocdate: February 23 2014 $
.Dt STPCPY 3
.Os
.Sh NAME
.Nm stpcpy ,
.Nm stpncpy
.Nd copy strings
.Sh SYNOPSIS
.In string.h
.Ft char *
.Fn stpcpy "char *dst" "const char *src"
.Ft char *
.Fn stpncpy "char *dst" "const char *src" "size_t len"
.Sh DESCRIPTION
The
.Fn stpcpy
and
.Fn stpncpy
functions copy the string
.Fa src
to
.Fa dst
(including the terminating
.Ql \e0
character).
.Pp
The
.Fn stpncpy
function copies not more than
.Fa len
characters into
.Fa dst ,
appending
.Ql \e0
characters if
.Fa src
is less than
.Fa len
characters long, and
.Em not
terminating
.Fa dst
if the length of
.Fa src
is greater than or equal to
.Fa len .
.Pp
If the
.Fa src
and
.Fa dst
strings overlap, the behavior is undefined.
.Sh RETURN VALUES
The
.Fn stpcpy
function returns a pointer to the terminating
.Ql \e0
character written into
.Fa dst .
.Pp
The
.Fn stpncpy
function returns a pointer to the first
.Ql \e0
character written into
.Fa dst ,
or to
.Fa &dst[len]
if the length of
.Fa src
is greater than or equal to
.Fa len .
.Sh EXAMPLES
The most common use of
.Fn stpcpy
is to build up a string from multiple elements.
The following example builds up a pathname from
directory and file components using
.Fn stpcpy :
.Bd -literal -offset indent
char *dir, *file, pname[PATH_MAX];

\&...

if (strlen(dir) + strlen("/") + strlen(file) >= sizeof(pname))
	goto toolong;
stpcpy(stpcpy(stpcpy(pname, dir), "/"), file);
.Ed
.Pp
However, the size check required to avoid a buffer overflow is error
prone since the check can become out of sync with the code that
performs the copy.
.Pp
One might expect that
.Fn stpncpy
could be safely used instead, but it suffers from the same defects as
.Fn strncpy .
The example below using
.Fn stpncpy
is even more prone to error and will not detect when truncation occurs:
.Bd -literal -offset indent
char *dir, *file, pname[PATH_MAX];
char *p1, *p2;

\&...

p1 = stpncpy(pname, dir, sizeof(pname) - 1);
p2 = stpncpy(p1, "/", sizeof(pname) - 1 - (p1 - pname));
stpncpy(p2, file, sizeof(pname) - 1 - (p2 - pname));
pname[sizeof(pname) - 1] = '\e0';
.Ed
.Pp
A safer (and simpler) approach is to use
.Fn snprintf :
.Bd -literal -offset indent
char *dir, *file, pname[PATH_MAX];
int len;

\&...

len = snprintf(pname, sizeof(pname), "%s/%s", dir, file);
if (len >= sizeof(pname))
	goto toolong;
.Ed
.Pp
In most cases, it is better to use
.Fn snprintf ,
.Fn strlcpy ,
or
.Fn strlcat .
.Sh SEE ALSO
.Xr snprintf 3 ,
.Xr strcpy 3 ,
.Xr strlcpy 3 ,
.Xr strncpy 3
.Sh STANDARDS
The
.Fn stpcpy
and
.Fn stpncpy
functions conform to
.St -p1003.1-2008 .
.Sh HISTORY
The function
.Fn stpcpy
first appeared in the Lattice C AmigaDOS compiler (1986 or earlier).
The function
.Fn stpncpy
first appeared in the GNU C library version 1.07 (1993).
Both functions have been available since
.Ox 5.1 .