.\" Copyright (c) 1990, 1991, 1993 .\" The Regents of the University of California. All rights reserved. .\" .\" This code is derived from software contributed to Berkeley by .\" Chris Torek and the American National Standards Committee X3, .\" on Information Processing Systems. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" 4. Neither the name of the University nor the names of its contributors .\" may be used to endorse or promote products derived from this software .\" without specific prior written permission. .\" .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" SUCH DAMAGE. .\" .\" @(#)strcpy.3 8.1 (Berkeley) 6/4/93 .\" $FreeBSD: src/lib/libc/string/strcpy.3,v 1.28 2009/04/07 13:42:53 trasz Exp $ .\" .Dd February 28, 2009 .Dt STRCPY 3 .Os .Sh NAME .Nm stpcpy, stpncpy, strcpy , strncpy .Nd copy strings .Sh LIBRARY .Lb libc .Sh SYNOPSIS .In string.h .Ft char * .Fo stpcpy .Fa "char *s1" .Fa "const char *s2" .Fc .Ft char * .Fo stpncpy .Fa "char *restrict s1" .Fa "const char *restrict s2" .Fa "size_t n" .Fc .Ft char * .Fo strcpy .Fa "char *restrict s1" .Fa "const char *restrict s2" .Fc .Ft char * .Fo strncpy .Fa "char *restrict s1" .Fa "const char *restrict s2" .Fa "size_t n" .Fc .Sh DESCRIPTION The .Fn stpcpy and .Fn strcpy functions copy the string .Fa s2 to .Fa s1 (including the terminating .Ql \e0 character). .Pp The .Fn stpncpy and .Fn strncpy functions copy at most .Fa n characters from .Fa s2 into .Fa s1 . If .Fa s2 is less than .Fa n characters long, the remainder of .Fa s1 is filled with .Ql \e0 characters. Otherwise, .Fa s1 is .Em not terminated. .Pp The source and destination strings should not overlap, as the behavior is undefined. .Sh RETURN VALUES The .Fn strcpy and .Fn strncpy functions return .Fa s1 . The .Fn stpcpy and .Fn stpncpy functions return a pointer to the terminating .Ql \e0 character of .Fa s1 . If .Fn stpncpy does not terminate .Fa s1 with a .Dv NUL character, it instead returns a pointer to .Li s1[n] (which does not necessarily refer to a valid memory location.) .Sh EXAMPLES The following sets .Va chararray to .Dq Li abc\e0\e0\e0 : .Bd -literal -offset indent char chararray; (void)strncpy(chararray, "abc", sizeof(chararray)); .Ed .Pp The following sets .Va chararray to .Dq Li abcdef : .Bd -literal -offset indent char chararray; (void)strncpy(chararray, "abcdefgh", sizeof(chararray)); .Ed .Pp Note that it does .Em not .Tn NUL terminate .Va chararray , because the length of the source string is greater than or equal to the length argument. .Pp The following copies as many characters from .Va input to .Va buf as will fit and .Tn NUL terminates the result. Because .Fn strncpy does .Em not guarantee to .Tn NUL terminate the string itself, this must be done explicitly. .Bd -literal -offset indent char buf; (void)strncpy(buf, input, sizeof(buf) - 1); buf[sizeof(buf) - 1] = '\e0'; .Ed .Pp This could be better achieved using .Xr strlcpy 3 , as shown in the following example: .Pp .Dl "(void)strlcpy(buf, input, sizeof(buf));" .Sh SECURITY CONSIDERATIONS The .Fn strcpy , .Fn strncpy , .Fn stpcpy , and .Fn stpncpy functions are easily misused in a manner which enables malicious users to arbitrarily change a running program's functionality through a buffer overflow attack. (See the FSA and .Sx EXAMPLES . ) .Pp It is recommended that .Xr strlcpy 3 be used instead as a way to avoid such problems. .Xr strlcpy 3 is not defined in any standards, but it has been adopted by most major libc implementations. .Sh SEE ALSO .Xr bcopy 3 , .Xr memccpy 3 , .Xr memcpy 3 , .Xr memmove 3 , .Xr strlcpy 3 , .Xr wcscpy 3 .Sh STANDARDS The .Fn strcpy and .Fn strncpy functions conform to .St -isoC . The .Fn stpcpy and .Fn stpncpy functions conform to .St -p1003.1-2008 . .Sh HISTORY The .Fn stpcpy function first appeared in .Fx 4.4 , and .Fn stpncpy was added in .Fx 8.0 .