View Source: strncpy(3) - Waikato Linux Users Group

Edit PageHistory Diff Info LikePages

!!!STRCPY
----
!!NAME


strcpy, strncpy - copy a string
!!SYNOPSIS


 #include <string.h>

 __char *strcpy(__''dest''__, const char *__''src''__);__

 __char *strncpy(char *__''dest''__, const char *__''src''__, size_t__ ''n''__);__

!!DESCRIPTION

The __strcpy()__ function copies the string pointed to by
''src'' (including the terminating `0' character) to the
array pointed to by ''dest''. The strings may not
overlap, and the destination string ''dest'' must be
large enough to receive the copy.

The __strncpy()__ function is similar, except that not
more than ''n'' bytes of ''src'' are copied. Thus, if
there is no null byte among the first ''n'' bytes of
''src'', the result wil not be
null-terminated.

In the case where the length of ''src'' is less than that
of ''n'', the remainder of ''dest'' will be padded
with nulls.

!!RETURN VALUE
The __strcpy()__ and __strncpy()__ functions return a
pointer to the destination string ''dest''.

!!BUGS
If the destination string of a __strcpy()__ is not large
enough (that is, if the programmer was stupid/lazy, and
failed to check the size before copying) then anything might
happen. Overflowing fixed length strings is a favourite
cracker technique.

!!CONFORMING TO
SVID 3, POSIX, BSD 4.3, ISO 9899

!!HISTORY
Rumour has it that the reason that strncpy() has such bizarre semantics (copying up to the entire length of the string and not leaving space for the terminating '0', and padding to the end of the buffer with '0's if it's shorter) come from the days when you could read/write a directory.  If you wanted to create a hardlink you opened the directory for writing and wrote the filename and the inode number into the directory.  The filename had to be exactly ''n'' bytes long and must be '0' padded (instead of just terminated), hence the strncpy() semantics.  It's far too late now to change the semantics to something more sane, so the [OpenBSD] people are advocating the use of strlcpy(3) instead.  Note, in high performance applications, strlcpy(3) is much faster than strncpy(3) as it doesn't waste time padding the entire string.

!!SEE ALSO
bcopy(3), memccpy(3), memcpy(3), memmove(3)

13 pages link to strncpy(3):

This page is a man page (or other imported legacy content). We are unable to automatically determine the license status of this page.

Last edited on Tuesday, May 24, 2005 6:48:42 pm by "HarunVos"

Edit PageHistory Diff Info LikePages