1.\" $OpenBSD: strlcpy.3,v 1.5 1999/06/06 15:17:32 aaron Exp $
2.\"
3.\" Copyright (c) 1998 Todd C. Miller <Todd.Miller@courtesan.com>
4.\" All rights reserved.
5.\"
6.\" Redistribution and use in source and binary forms, with or without
7.\" modification, are permitted provided that the following conditions
8.\" are met:
9.\" 1. Redistributions of source code must retain the above copyright
10.\" notice, this list of conditions and the following disclaimer.
11.\" 2. Redistributions in binary form must reproduce the above copyright
12.\" notice, this list of conditions and the following disclaimer in the
13.\" documentation and/or other materials provided with the distribution.
14.\" 3. The name of the author may not be used to endorse or promote products
15.\" derived from this software without specific prior written permission.
16.\"
17.\" THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES,
18.\" INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
19.\" AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
20.\" THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
21.\" EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
22.\" PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
23.\" OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
24.\" WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
25.\" OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
26.\" ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
27.\"
| 1.\" $OpenBSD: strlcpy.3,v 1.5 1999/06/06 15:17:32 aaron Exp $
2.\"
3.\" Copyright (c) 1998 Todd C. Miller <Todd.Miller@courtesan.com>
4.\" All rights reserved.
5.\"
6.\" Redistribution and use in source and binary forms, with or without
7.\" modification, are permitted provided that the following conditions
8.\" are met:
9.\" 1. Redistributions of source code must retain the above copyright
10.\" notice, this list of conditions and the following disclaimer.
11.\" 2. Redistributions in binary form must reproduce the above copyright
12.\" notice, this list of conditions and the following disclaimer in the
13.\" documentation and/or other materials provided with the distribution.
14.\" 3. The name of the author may not be used to endorse or promote products
15.\" derived from this software without specific prior written permission.
16.\"
17.\" THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES,
18.\" INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
19.\" AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
20.\" THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
21.\" EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
22.\" PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
23.\" OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
24.\" WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
25.\" OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
26.\" ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
27.\"
|
28.\" $FreeBSD: head/lib/libc/string/strlcpy.3 108037 2002-12-18 12:45:11Z ru $
| 28.\" $FreeBSD: head/lib/libc/string/strlcpy.3 131504 2004-07-02 23:52:20Z ru $
|
29.\"
30.Dd June 22, 1998
31.Dt STRLCPY 3
32.Os
33.Sh NAME
34.Nm strlcpy ,
35.Nm strlcat
36.Nd size-bounded string copying and concatenation
37.Sh LIBRARY
38.Lb libc
39.Sh SYNOPSIS
40.In string.h
41.Ft size_t
42.Fn strlcpy "char *dst" "const char *src" "size_t size"
43.Ft size_t
44.Fn strlcat "char *dst" "const char *src" "size_t size"
45.Sh DESCRIPTION
46The
47.Fn strlcpy
48and
49.Fn strlcat
| 29.\"
30.Dd June 22, 1998
31.Dt STRLCPY 3
32.Os
33.Sh NAME
34.Nm strlcpy ,
35.Nm strlcat
36.Nd size-bounded string copying and concatenation
37.Sh LIBRARY
38.Lb libc
39.Sh SYNOPSIS
40.In string.h
41.Ft size_t
42.Fn strlcpy "char *dst" "const char *src" "size_t size"
43.Ft size_t
44.Fn strlcat "char *dst" "const char *src" "size_t size"
45.Sh DESCRIPTION
46The
47.Fn strlcpy
48and
49.Fn strlcat
|
50functions copy and concatenate strings respectively. They are designed
| 50functions copy and concatenate strings respectively.
51They are designed
|
51to be safer, more consistent, and less error prone replacements for
52.Xr strncpy 3
53and
54.Xr strncat 3 .
55Unlike those functions,
56.Fn strlcpy
57and
58.Fn strlcat
59take the full size of the buffer (not just the length) and guarantee to
60NUL-terminate the result (as long as
61.Fa size
62is larger than 0 or, in the case of
63.Fn strlcat ,
64as long as there is at least one byte free in
65.Fa dst ) .
66Note that you should include a byte for the NUL in
67.Fa size .
68Also note that
69.Fn strlcpy
70and
71.Fn strlcat
72only operate on true
73.Dq C
74strings.
75This means that for
76.Fn strlcpy
77.Fa src
78must be NUL-terminated and for
79.Fn strlcat
80both
81.Fa src
82and
83.Fa dst
84must be NUL-terminated.
85.Pp
86The
87.Fn strlcpy
88function copies up to
89.Fa size
90- 1 characters from the NUL-terminated string
91.Fa src
92to
93.Fa dst ,
94NUL-terminating the result.
95.Pp
96The
97.Fn strlcat
98function appends the NUL-terminated string
99.Fa src
100to the end of
101.Fa dst .
102It will append at most
103.Fa size
104- strlen(dst) - 1 bytes, NUL-terminating the result.
105.Sh RETURN VALUES
106The
107.Fn strlcpy
108and
109.Fn strlcat
110functions return the total length of the string they tried to
| 52to be safer, more consistent, and less error prone replacements for
53.Xr strncpy 3
54and
55.Xr strncat 3 .
56Unlike those functions,
57.Fn strlcpy
58and
59.Fn strlcat
60take the full size of the buffer (not just the length) and guarantee to
61NUL-terminate the result (as long as
62.Fa size
63is larger than 0 or, in the case of
64.Fn strlcat ,
65as long as there is at least one byte free in
66.Fa dst ) .
67Note that you should include a byte for the NUL in
68.Fa size .
69Also note that
70.Fn strlcpy
71and
72.Fn strlcat
73only operate on true
74.Dq C
75strings.
76This means that for
77.Fn strlcpy
78.Fa src
79must be NUL-terminated and for
80.Fn strlcat
81both
82.Fa src
83and
84.Fa dst
85must be NUL-terminated.
86.Pp
87The
88.Fn strlcpy
89function copies up to
90.Fa size
91- 1 characters from the NUL-terminated string
92.Fa src
93to
94.Fa dst ,
95NUL-terminating the result.
96.Pp
97The
98.Fn strlcat
99function appends the NUL-terminated string
100.Fa src
101to the end of
102.Fa dst .
103It will append at most
104.Fa size
105- strlen(dst) - 1 bytes, NUL-terminating the result.
106.Sh RETURN VALUES
107The
108.Fn strlcpy
109and
110.Fn strlcat
111functions return the total length of the string they tried to
|
111create. For
| 112create.
113For
|
112.Fn strlcpy
113that means the length of
114.Fa src .
115For
116.Fn strlcat
117that means the initial length of
118.Fa dst
119plus
120the length of
121.Fa src .
122While this may seem somewhat confusing it was done to make
123truncation detection simple.
124.Pp
125Note however, that if
126.Fn strlcat
127traverses
128.Fa size
129characters without finding a NUL, the length of the string is considered
130to be
131.Fa size
132and the destination string will not be NUL-terminated (since there was
133no space for the NUL).
134This keeps
135.Fn strlcat
136from running off the end of a string.
137In practice this should not happen (as it means that either
138.Fa size
139is incorrect or that
140.Fa dst
141is not a proper
142.Dq C
143string).
144The check exists to prevent potential security problems in incorrect code.
145.Sh EXAMPLES
146The following code fragment illustrates the simple case:
147.Bd -literal -offset indent
148char *s, *p, buf[BUFSIZ];
149
150\&...
151
152(void)strlcpy(buf, s, sizeof(buf));
153(void)strlcat(buf, p, sizeof(buf));
154.Ed
155.Pp
156To detect truncation, perhaps while building a pathname, something
157like the following might be used:
158.Bd -literal -offset indent
159char *dir, *file, pname[MAXPATHLEN];
160
161\&...
162
163if (strlcpy(pname, dir, sizeof(pname)) >= sizeof(pname))
164 goto toolong;
165if (strlcat(pname, file, sizeof(pname)) >= sizeof(pname))
166 goto toolong;
167.Ed
168.Pp
169Since we know how many characters we copied the first time, we can
170speed things up a bit by using a copy instead of an append:
171.Bd -literal -offset indent
172char *dir, *file, pname[MAXPATHLEN];
173size_t n;
174
175\&...
176
177n = strlcpy(pname, dir, sizeof(pname));
178if (n >= sizeof(pname))
179 goto toolong;
180if (strlcpy(pname + n, file, sizeof(pname) - n) >= sizeof(pname) - n)
181 goto toolong;
182.Ed
183.Pp
184However, one may question the validity of such optimizations, as they
185defeat the whole purpose of
186.Fn strlcpy
187and
188.Fn strlcat .
189As a matter of fact, the first version of this manual page got it wrong.
190.Sh SEE ALSO
191.Xr snprintf 3 ,
192.Xr strncat 3 ,
193.Xr strncpy 3
194.Sh HISTORY
195The
196.Fn strlcpy
197and
198.Fn strlcat
199functions first appeared in
200.Ox 2.4 ,
201and made their appearance in
202.Fx 3.3 .
| 114.Fn strlcpy
115that means the length of
116.Fa src .
117For
118.Fn strlcat
119that means the initial length of
120.Fa dst
121plus
122the length of
123.Fa src .
124While this may seem somewhat confusing it was done to make
125truncation detection simple.
126.Pp
127Note however, that if
128.Fn strlcat
129traverses
130.Fa size
131characters without finding a NUL, the length of the string is considered
132to be
133.Fa size
134and the destination string will not be NUL-terminated (since there was
135no space for the NUL).
136This keeps
137.Fn strlcat
138from running off the end of a string.
139In practice this should not happen (as it means that either
140.Fa size
141is incorrect or that
142.Fa dst
143is not a proper
144.Dq C
145string).
146The check exists to prevent potential security problems in incorrect code.
147.Sh EXAMPLES
148The following code fragment illustrates the simple case:
149.Bd -literal -offset indent
150char *s, *p, buf[BUFSIZ];
151
152\&...
153
154(void)strlcpy(buf, s, sizeof(buf));
155(void)strlcat(buf, p, sizeof(buf));
156.Ed
157.Pp
158To detect truncation, perhaps while building a pathname, something
159like the following might be used:
160.Bd -literal -offset indent
161char *dir, *file, pname[MAXPATHLEN];
162
163\&...
164
165if (strlcpy(pname, dir, sizeof(pname)) >= sizeof(pname))
166 goto toolong;
167if (strlcat(pname, file, sizeof(pname)) >= sizeof(pname))
168 goto toolong;
169.Ed
170.Pp
171Since we know how many characters we copied the first time, we can
172speed things up a bit by using a copy instead of an append:
173.Bd -literal -offset indent
174char *dir, *file, pname[MAXPATHLEN];
175size_t n;
176
177\&...
178
179n = strlcpy(pname, dir, sizeof(pname));
180if (n >= sizeof(pname))
181 goto toolong;
182if (strlcpy(pname + n, file, sizeof(pname) - n) >= sizeof(pname) - n)
183 goto toolong;
184.Ed
185.Pp
186However, one may question the validity of such optimizations, as they
187defeat the whole purpose of
188.Fn strlcpy
189and
190.Fn strlcat .
191As a matter of fact, the first version of this manual page got it wrong.
192.Sh SEE ALSO
193.Xr snprintf 3 ,
194.Xr strncat 3 ,
195.Xr strncpy 3
196.Sh HISTORY
197The
198.Fn strlcpy
199and
200.Fn strlcat
201functions first appeared in
202.Ox 2.4 ,
203and made their appearance in
204.Fx 3.3 .
|