1.\" $OpenBSD: strncpy.3,v 1.1 2013/12/19 20:52:37 millert Exp $ 2.\" 3.\" Copyright (c) 1990, 1991 The Regents of the University of California. 4.\" All rights reserved. 5.\" 6.\" This code is derived from software contributed to Berkeley by 7.\" Chris Torek and the American National Standards Committee X3, 8.\" on Information Processing Systems. 9.\" 10.\" Redistribution and use in source and binary forms, with or without 11.\" modification, are permitted provided that the following conditions 12.\" are met: 13.\" 1. Redistributions of source code must retain the above copyright 14.\" notice, this list of conditions and the following disclaimer. 15.\" 2. Redistributions in binary form must reproduce the above copyright 16.\" notice, this list of conditions and the following disclaimer in the 17.\" documentation and/or other materials provided with the distribution. 18.\" 3. Neither the name of the University nor the names of its contributors 19.\" may be used to endorse or promote products derived from this software 20.\" without specific prior written permission. 21.\" 22.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 23.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 24.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 25.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 26.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 27.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 28.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 29.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 31.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32.\" SUCH DAMAGE. 33.\" 34.Dd $Mdocdate: December 19 2013 $ 35.Dt STRNCPY 3 36.Os 37.Sh NAME 38.Nm strncpy 39.Nd copy part of a string to another 40.Sh SYNOPSIS 41.In string.h 42.Ft char * 43.Fn strncpy "char *dst" "const char *src" "size_t len" 44.Sh DESCRIPTION 45The 46.Fn strncpy 47function copies not more than 48.Fa len 49characters from the string 50.Fa src 51to 52.Fa dst . 53If 54.Fa src 55is less than 56.Fa len 57characters long, 58it appends 59.Ql \e0 60characters for the rest of 61.Fa len . 62If the length of 63.Fa src 64is greater than or equal to 65.Fa len , 66.Fa dst 67will 68.Em not 69be NUL-terminated. 70.Pp 71If the 72.Fa src 73and 74.Fa dst 75strings overlap, the behavior is undefined. 76.Sh RETURN VALUES 77The 78.Fn strncpy 79function returns 80.Fa dst . 81.Sh EXAMPLES 82The following sets 83.Va chararray 84to 85.Dq abc\e0\e0\e0 : 86.Bd -literal -offset indent 87(void)strncpy(chararray, "abc", 6); 88.Ed 89.Pp 90The following sets 91.Va chararray 92to 93.Dq abcdef 94and does 95.Em not 96NUL terminate 97.Va chararray 98because the length of the source string is greater than or equal to the 99length parameter. 100.Fn strncpy 101.Em only 102NUL terminates the destination string when the length of the source 103string is less than the length parameter. 104.Bd -literal -offset indent 105(void)strncpy(chararray, "abcdefgh", 6); 106.Ed 107.Pp 108The following copies as many characters from 109.Va input 110to 111.Va buf 112as will fit and NUL terminates the result. 113Because 114.Fn strncpy 115does 116.Em not 117guarantee to NUL terminate the string itself, it must be done by hand. 118.Bd -literal -offset indent 119char buf[BUFSIZ]; 120 121(void)strncpy(buf, input, sizeof(buf) - 1); 122buf[sizeof(buf) - 1] = '\e0'; 123.Ed 124.Pp 125Note that 126.Xr strlcpy 3 127is a better choice for this kind of operation. 128The equivalent using 129.Xr strlcpy 3 130is simply: 131.Bd -literal -offset indent 132(void)strlcpy(buf, input, sizeof(buf)); 133.Ed 134.Sh SEE ALSO 135.Xr bcopy 3 , 136.Xr memccpy 3 , 137.Xr memcpy 3 , 138.Xr memmove 3 , 139.Xr strcat 3 , 140.Xr strlcpy 3 , 141.Xr strncat 3 , 142.Xr wcscpy 3 , 143.Xr wcslcpy 3 144.Sh STANDARDS 145The 146.Fn strncpy 147function conforms to 148.St -ansiC . 149.Sh HISTORY 150The 151.Fn strncpy 152function first appeared in 153.At v7 . 154