mirror of
https://gitlab.freedesktop.org/libbsd/libbsd.git
synced 2025-01-09 19:27:42 +01:00
f20e6972b3
This should guarantee that even if the system provides or will provide native implementations of these functions, we will not have file conflicts.
192 lines
4.4 KiB
Plaintext
192 lines
4.4 KiB
Plaintext
.\" $OpenBSD: strlcpy.3,v 1.18 2005/08/06 03:24:19 jaredy Exp $
|
|
.\"
|
|
.\" Copyright (c) 1998, 2000 Todd C. Miller <Todd.Miller@courtesan.com>
|
|
.\"
|
|
.\" Permission to use, copy, modify, and distribute this software for any
|
|
.\" purpose with or without fee is hereby granted, provided that the above
|
|
.\" copyright notice and this permission notice appear in all copies.
|
|
.\"
|
|
.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
|
|
.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
|
|
.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
|
|
.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
|
|
.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
|
|
.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
|
|
.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
|
|
.\"
|
|
.Dd $Mdocdate: May 31 2007 $
|
|
.Dt STRLCPY 3
|
|
.Os
|
|
.Sh NAME
|
|
.Nm strlcpy ,
|
|
.Nm strlcat
|
|
.Nd size-bounded string copying and concatenation
|
|
.Sh LIBRARY
|
|
.ds str-Lb-libbsd Utility functions from BSD systems (libbsd, \-lbsd)
|
|
.Lb libbsd
|
|
.Sh SYNOPSIS
|
|
.In bsd/string.h
|
|
.Ft size_t
|
|
.Fn strlcpy "char *dst" "const char *src" "size_t size"
|
|
.Ft size_t
|
|
.Fn strlcat "char *dst" "const char *src" "size_t size"
|
|
.Sh DESCRIPTION
|
|
The
|
|
.Fn strlcpy
|
|
and
|
|
.Fn strlcat
|
|
functions copy and concatenate strings respectively.
|
|
They are designed
|
|
to be safer, more consistent, and less error prone replacements for
|
|
.Xr strncpy 3
|
|
and
|
|
.Xr strncat 3 .
|
|
Unlike those functions,
|
|
.Fn strlcpy
|
|
and
|
|
.Fn strlcat
|
|
take the full size of the buffer (not just the length) and guarantee to
|
|
NUL-terminate the result (as long as
|
|
.Fa size
|
|
is larger than 0 or, in the case of
|
|
.Fn strlcat ,
|
|
as long as there is at least one byte free in
|
|
.Fa dst ) .
|
|
Note that a byte for the NUL should be included in
|
|
.Fa size .
|
|
Also note that
|
|
.Fn strlcpy
|
|
and
|
|
.Fn strlcat
|
|
only operate on true
|
|
.Dq C
|
|
strings.
|
|
This means that for
|
|
.Fn strlcpy
|
|
.Fa src
|
|
must be NUL-terminated and for
|
|
.Fn strlcat
|
|
both
|
|
.Fa src
|
|
and
|
|
.Fa dst
|
|
must be NUL-terminated.
|
|
.Pp
|
|
The
|
|
.Fn strlcpy
|
|
function copies up to
|
|
.Fa size
|
|
- 1 characters from the NUL-terminated string
|
|
.Fa src
|
|
to
|
|
.Fa dst ,
|
|
NUL-terminating the result.
|
|
.Pp
|
|
The
|
|
.Fn strlcat
|
|
function appends the NUL-terminated string
|
|
.Fa src
|
|
to the end of
|
|
.Fa dst .
|
|
It will append at most
|
|
.Fa size
|
|
- strlen(dst) - 1 bytes, NUL-terminating the result.
|
|
.Sh RETURN VALUES
|
|
The
|
|
.Fn strlcpy
|
|
and
|
|
.Fn strlcat
|
|
functions return the total length of the string they tried to create.
|
|
For
|
|
.Fn strlcpy
|
|
that means the length of
|
|
.Fa src .
|
|
For
|
|
.Fn strlcat
|
|
that means the initial length of
|
|
.Fa dst
|
|
plus
|
|
the length of
|
|
.Fa src .
|
|
While this may seem somewhat confusing, it was done to make
|
|
truncation detection simple.
|
|
.Pp
|
|
Note, however, that if
|
|
.Fn strlcat
|
|
traverses
|
|
.Fa size
|
|
characters without finding a NUL, the length of the string is considered
|
|
to be
|
|
.Fa size
|
|
and the destination string will not be NUL-terminated (since there was
|
|
no space for the NUL).
|
|
This keeps
|
|
.Fn strlcat
|
|
from running off the end of a string.
|
|
In practice this should not happen (as it means that either
|
|
.Fa size
|
|
is incorrect or that
|
|
.Fa dst
|
|
is not a proper
|
|
.Dq C
|
|
string).
|
|
The check exists to prevent potential security problems in incorrect code.
|
|
.Sh EXAMPLES
|
|
The following code fragment illustrates the simple case:
|
|
.Bd -literal -offset indent
|
|
char *s, *p, buf[BUFSIZ];
|
|
|
|
\&...
|
|
|
|
(void)strlcpy(buf, s, sizeof(buf));
|
|
(void)strlcat(buf, p, sizeof(buf));
|
|
.Ed
|
|
.Pp
|
|
To detect truncation, perhaps while building a pathname, something
|
|
like the following might be used:
|
|
.Bd -literal -offset indent
|
|
char *dir, *file, pname[MAXPATHLEN];
|
|
|
|
\&...
|
|
|
|
if (strlcpy(pname, dir, sizeof(pname)) >= sizeof(pname))
|
|
goto toolong;
|
|
if (strlcat(pname, file, sizeof(pname)) >= sizeof(pname))
|
|
goto toolong;
|
|
.Ed
|
|
.Pp
|
|
Since it is known how many characters were copied the first time, things
|
|
can be sped up a bit by using a copy instead of an append:
|
|
.Bd -literal -offset indent
|
|
char *dir, *file, pname[MAXPATHLEN];
|
|
size_t n;
|
|
|
|
\&...
|
|
|
|
n = strlcpy(pname, dir, sizeof(pname));
|
|
if (n >= sizeof(pname))
|
|
goto toolong;
|
|
if (strlcpy(pname + n, file, sizeof(pname) - n) >= sizeof(pname) - n)
|
|
goto toolong;
|
|
.Ed
|
|
.Pp
|
|
However, one may question the validity of such optimizations, as they
|
|
defeat the whole purpose of
|
|
.Fn strlcpy
|
|
and
|
|
.Fn strlcat .
|
|
As a matter of fact, the first version of this manual page got it wrong.
|
|
.Sh SEE ALSO
|
|
.Xr snprintf 3 ,
|
|
.Xr strncat 3 ,
|
|
.Xr strncpy 3
|
|
.Sh HISTORY
|
|
The
|
|
.Fn strlcpy
|
|
and
|
|
.Fn strlcat
|
|
functions first appeared in
|
|
.Ox 2.4 ,
|
|
and made their appearance in
|
|
.Fx 3.3 .
|