1.\" $NetBSD: strlcpy.3,v 1.2 1999/09/08 22:56:56 lukem Exp $ 2.\" from OpenBSD: strlcpy.3,v 1.6 1999/09/04 02:22:46 pjanzen Exp 3.\" 4.\" Copyright (c) 1998 Todd C. Miller <Todd.Miller@courtesan.com> 5.\" All rights reserved. 6.\" 7.\" Redistribution and use in source and binary forms, with or without 8.\" modification, are permitted provided that the following conditions 9.\" are met: 10.\" 1. Redistributions of source code must retain the above copyright 11.\" notice, this list of conditions and the following disclaimer. 12.\" 2. Redistributions in binary form must reproduce the above copyright 13.\" notice, this list of conditions and the following disclaimer in the 14.\" documentation and/or other materials provided with the distribution. 15.\" 3. The name of the author may not be used to endorse or promote products 16.\" derived from this software without specific prior written permission. 17.\" 18.\" THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, 19.\" INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY 20.\" AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL 21.\" THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, 22.\" EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, 23.\" PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; 24.\" OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, 25.\" WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR 26.\" OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF 27.\" ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 28.\" 29.Dd September 9, 1999 30.Dt STRLCPY 3 31.Os 32.Sh NAME 33.Nm strlcpy , 34.Nm strlcat 35.Nd size-bounded string copying and concatenation 36.Sh SYNOPSIS 37.Fd #include <string.h> 38.Ft size_t 39.Fn strlcpy "char *dst" "const char *src" "size_t size" 40.Ft size_t 41.Fn strlcat "char *dst" "const char *src" "size_t size" 42.Sh DESCRIPTION 43The 44.Fn strlcpy 45and 46.Fn strlcat 47functions copy and concatenate strings respectively. They are designed 48to be safer, more consistent, and less error prone replacements for 49.Xr strncpy 3 50and 51.Xr strncat 3 . 52Unlike those functions, 53.Fn strlcpy 54and 55.Fn strlcat 56take the full size of the buffer (not just the length) and guarantee to 57NUL-terminate the result (as long as 58.Fa size 59is larger than 0). Note that you should include a byte for the NUL in 60.Fa size . 61.Pp 62The 63.Fn strlcpy 64function copies up to 65.Fa size 66- 1 characters from the NUL-terminated string 67.Fa src 68to 69.Fa dst , 70NUL-terminating the result. 71.Pp 72The 73.Fn strlcat 74function appends the NUL-terminated string 75.Fa src 76to the end of 77.Fa dst . 78It will append at most 79.Fa size 80- strlen(dst) - 1 bytes, NUL-terminating the result. 81.Sh RETURN VALUES 82The 83.Fn strlcpy 84and 85.Fn strlcat 86functions return the total length of the string they tried to 87create. For 88.Fn strlcpy 89that means the length of 90.Fa src . 91For 92.Fn strlcat 93that means the initial length of 94.Fa dst 95plus 96the length of 97.Fa src . 98While this may seem somewhat confusing it was done to make 99truncation detection simple. 100.Sh EXAMPLES 101The following code fragment illustrates the simple case: 102.Bd -literal -offset indent 103char *s, *p, buf[BUFSIZ]; 104 105\&... 106 107(void)strlcpy(buf, s, sizeof(buf)); 108(void)strlcat(buf, p, sizeof(buf)); 109.Ed 110.Pp 111To detect truncation, perhaps while building a pathname, something 112like the following might be used: 113.Bd -literal -offset indent 114char *dir, *file, pname[MAXPATHNAMELEN]; 115 116\&... 117 118if (strlcpy(pname, dir, sizeof(pname)) >= sizeof(pname)) 119 goto toolong; 120if (strlcat(pname, file, sizeof(pname)) >= sizeof(pname)) 121 goto toolong; 122.Ed 123.Pp 124Since we know how many characters we copied the first time, we can 125speed things up a bit by using a copy instead on an append: 126.Bd -literal -offset indent 127char *dir, *file, pname[MAXPATHNAMELEN]; 128size_t n; 129 130\&... 131 132n = strlcpy(pname, dir, sizeof(pname)); 133if (n >= sizeof(pname)) 134 goto toolong; 135if (strlcpy(pname + n, file, sizeof(pname) - n) >= sizeof(pname) - n) 136 goto toolong; 137.Ed 138.Pp 139However, one may question the validity of such optimizations, as they 140defeat the whole purpose of 141.Fn strlcpy 142and 143.Fn strlcat . 144As a matter of fact, the first version of this manual page got it wrong. 145.Sh SEE ALSO 146.Xr snprintf 3 , 147.Xr strncat 3 , 148.Xr strncpy 3 149