b7e471c2b2
In the DESCRIPTION, put the more commonly used functions first in the corresponding sentence, to help catch the eye. Pull out the note about overlapping buffers to its own paragraph, as it applies to all routines documented by this page. Emphasize the potentially surprising strncpy(3) behavior of zero-filling the remainder of a buffer larger than the source string. Encourage strlcpy use; remove portability note about strlcpy(3). Adapting a strlcpy-using code base to a platform that does not provide strlcpy in libc is so trivial as to not be worth mentioning. (Just copy strlcpy.c out of any BSD libc, or include and link the pre-packaged libbsd library on non-BSD platforms.) Likewise, expand the page's warning about ease of potential misuse to cover all functions documented herein, and explicitly suggest using strlcpy most of the time. The text was mostly cribbed from a similar suggestion in gets(3). Finally, document the remaining valid use of strncpy -- the rare fixed-length record with no expectation of nul-termination. Sponsored by: Dell EMC Isilon
234 lines
4.9 KiB
Groff
234 lines
4.9 KiB
Groff
.\" Copyright (c) 1990, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" This code is derived from software contributed to Berkeley by
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.\" Chris Torek and the American National Standards Committee X3,
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.\" on Information Processing Systems.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)strcpy.3 8.1 (Berkeley) 6/4/93
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.\" $FreeBSD$
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.\"
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.Dd June 6, 2018
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.Dt STRCPY 3
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.Os
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.Sh NAME
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.Nm stpcpy ,
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.Nm stpncpy ,
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.Nm strcpy ,
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.Nm strncpy
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.Nd copy strings
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In string.h
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.Ft char *
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.Fn stpcpy "char * restrict dst" "const char * restrict src"
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.Ft char *
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.Fn stpncpy "char * restrict dst" "const char * restrict src" "size_t len"
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.Ft char *
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.Fn strcpy "char * restrict dst" "const char * restrict src"
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.Ft char *
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.Fn strncpy "char * restrict dst" "const char * restrict src" "size_t len"
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.Sh DESCRIPTION
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The
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.Fn strcpy
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and
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.Fn stpcpy
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functions
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copy the string
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.Fa src
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to
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.Fa dst
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(including the terminating
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.Ql \e0
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character.)
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.Pp
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The
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.Fn strncpy
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and
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.Fn stpncpy
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functions copy at most
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.Fa len
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characters from
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.Fa src
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into
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.Fa dst .
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.Bf Sy
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If
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.Fa src
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is less than
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.Fa len
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characters long,
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the remainder of
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.Fa dst
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is filled with
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.Ql \e0
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characters.
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.Ef
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Otherwise,
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.Fa dst
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is
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.Em not
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terminated.
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.Pp
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For all of
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.Fn strcpy ,
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.Fn strncpy ,
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.Fn stpcpy ,
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and
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.Fn stpncpy ,
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the result is undefined
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if
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.Fa src
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and
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.Fa dst
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overlap.
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.Sh RETURN VALUES
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The
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.Fn strcpy
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and
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.Fn strncpy
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functions
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return
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.Fa dst .
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The
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.Fn stpcpy
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and
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.Fn stpncpy
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functions return a pointer to the terminating
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.Ql \e0
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character of
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.Fa dst .
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If
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.Fn stpncpy
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does not terminate
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.Fa dst
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with a
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.Dv NUL
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character, it instead returns a pointer to
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.Li dst[n]
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(which does not necessarily refer to a valid memory location.)
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.Sh EXAMPLES
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The following sets
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.Va chararray
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to
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.Dq Li abc\e0\e0\e0 :
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.Bd -literal -offset indent
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char chararray[6];
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(void)strncpy(chararray, "abc", sizeof(chararray));
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.Ed
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.Pp
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The following sets
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.Va chararray
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to
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.Dq Li abcdef :
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.Bd -literal -offset indent
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char chararray[6];
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(void)strncpy(chararray, "abcdefgh", sizeof(chararray));
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.Ed
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.Pp
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Note that it does
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.Em not
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.Tn NUL
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terminate
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.Va chararray
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because the length of the source string is greater than or equal
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to the length argument.
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.Pp
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The following copies as many characters from
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.Va input
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to
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.Va buf
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as will fit and
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.Tn NUL
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terminates the result.
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Because
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.Fn strncpy
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does
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.Em not
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guarantee to
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.Tn NUL
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terminate the string itself, this must be done explicitly.
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.Bd -literal -offset indent
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char buf[1024];
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(void)strncpy(buf, input, sizeof(buf) - 1);
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buf[sizeof(buf) - 1] = '\e0';
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.Ed
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.Pp
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This could be better achieved using
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.Xr strlcpy 3 ,
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as shown in the following example:
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.Pp
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.Dl "(void)strlcpy(buf, input, sizeof(buf));"
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.Sh SEE ALSO
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.Xr bcopy 3 ,
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.Xr memccpy 3 ,
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.Xr memcpy 3 ,
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.Xr memmove 3 ,
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.Xr strlcpy 3 ,
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.Xr wcscpy 3
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.Sh STANDARDS
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The
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.Fn strcpy
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and
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.Fn strncpy
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functions
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conform to
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.St -isoC .
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The
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.Fn stpcpy
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and
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.Fn stpncpy
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functions conform to
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.St -p1003.1-2008 .
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.Sh HISTORY
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The
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.Fn stpcpy
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function first appeared in
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.Fx 4.4 ,
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and
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.Fn stpncpy
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was added in
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.Fx 8.0 .
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.Sh SECURITY CONSIDERATIONS
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All of the functions documented in this manual page are easily misused in a
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manner which enables malicious users to arbitrarily change a running program's
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functionality through a buffer overflow attack.
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.Pp
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It is strongly suggested that the
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.Fn strlcpy
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function be used in almost all cases.
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.Pp
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For some, but not all, fixed-length records, non-terminated strings may be both
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valid and desirable.
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In that specific case, the
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.Fn strncpy
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function may be most sensible.
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