mirror of https://github.com/mkerrisk/man-pages
137 lines
3.8 KiB
Groff
137 lines
3.8 KiB
Groff
.\" Copyright (C) 1993 David Metcalfe (david@prism.demon.co.uk)
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.\"
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\"
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.\" References consulted:
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.\" Linux libc source code
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.\" Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
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.\" 386BSD man pages
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.\" Modified Sat Jul 24 18:06:49 1993 by Rik Faith (faith@cs.unc.edu)
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.\" Modified Fri Aug 25 23:17:51 1995 by Andries Brouwer (aeb@cwi.nl)
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.\" Modified Wed Dec 18 00:47:18 1996 by Andries Brouwer (aeb@cwi.nl)
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.\" 2007-06-15, Marc Boyer <marc.boyer@enseeiht.fr> + mtk
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.\" Improve discussion of strncpy().
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.\"
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.TH STRCPY 3 2007-06-15 "GNU" "Linux Programmer's Manual"
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.SH NAME
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strcpy, strncpy \- copy a string
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.SH SYNOPSIS
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.nf
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.B #include <string.h>
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.sp
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.BI "char *strcpy(char *" dest ", const char *" src );
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.sp
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.BI "char *strncpy(char *" dest ", const char *" src ", size_t " n );
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.fi
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.SH DESCRIPTION
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The
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.BR strcpy ()
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function copies the string pointed to by \fIsrc\fP,
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including the terminating null byte (\(aq\\0\(aq),
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to the buffer pointed to by \fIdest\fP.
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The strings may not overlap, and the destination string
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\fIdest\fP must be large enough to receive the copy.
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.PP
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The
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.BR strncpy ()
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function is similar, except that at most
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\fIn\fP bytes of \fIsrc\fP are copied.
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.BR Warning :
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If there is no null byte
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among the first \fIn\fP bytes of \fIsrc\fP,
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the string placed in \fIdest\fP will not be null terminated.
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.PP
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If the length of
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.I src
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is less than
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.IR n ,
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.BR strncpy ()
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pads the remainder of
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.I dest
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with null bytes.
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.PP
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A simple implementation of
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.BR strncpy ()
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might be:
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.in +4n
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.nf
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char*
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strncpy(char *dest, const char *src, size_t n){
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size_t i;
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for (i = 0 ; i < n && src[i] != \(aq\\0\(aq ; i++)
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dest[i] = src[i];
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for ( ; i < n ; i++)
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dest[i] = \(aq\\0\(aq;
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return dest;
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}
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.fi
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.in
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.SH "RETURN VALUE"
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The
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.BR strcpy ()
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and
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.BR strncpy ()
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functions return a pointer to
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the destination string \fIdest\fP.
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.SH "CONFORMING TO"
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SVr4, 4.3BSD, C89, C99.
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.SH NOTES
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Some programmers consider
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.BR strncpy ()
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to be inefficient and error prone.
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If the programmer knows (i.e., includes code to test!)
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that the size of \fIdest\fP is greater than
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the length of \fIsrc\fP, then
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.BR strcpy ()
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can be used.
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If there is no terminating null byte in the first \fIn\fP
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characters of \fIsrc\fP,
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.BR strncpy ()
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produces an unterminated string in \fIdest\fP.
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Programmers often prevent this mistake by forcing termination
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as follows:
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.in +4n
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.nf
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strncpy(buf, str, n);
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if (n > 0)
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buf[n - 1]= \(aq\\0\(aq;
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.fi
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.in
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.SH BUGS
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If the destination string of a
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.BR strcpy ()
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is not large enough
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(that is, if the programmer was stupid or lazy, and failed to check
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the size before copying) then anything might happen.
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Overflowing fixed length strings is a favorite cracker technique.
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.SH "SEE ALSO"
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.BR bcopy (3),
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.BR memccpy (3),
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.BR memcpy (3),
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.BR memmove (3),
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.BR wcscpy (3),
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.BR wcsncpy (3)
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