Date: Sun, 16 Mar 2003 18:17:52 -0700 (MST) From: "M. Warner Losh" <imp@bsdimp.com> To: phk@phk.freebsd.dk Cc: arch@FreeBSD.ORG Subject: Re: memcpy() with specified direction of copying ? Message-ID: <20030316.181752.16867058.imp@bsdimp.com> In-Reply-To: <9357.1047847012@critter.freebsd.dk> References: <9357.1047847012@critter.freebsd.dk>
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In message: <9357.1047847012@critter.freebsd.dk>
Poul-Henning Kamp <phk@phk.freebsd.dk> writes:
:
: Is there any standard which has provided an api for mandating the
: direction of copying from a memcpy() like function ?
:
: As I read our man-page, there is no way to know of memcpy() copies
: from the start and forward or from the end and backward through the
: two areas.
memcpy is not defined when overlapping strings are concerned. It is
allowed to screw them up in whatever ways are a side effect of the
fastest way to copy memory is. memmove is well defined here. It is
slower, but guaranteed to work on overlapping strings. A string here
is a hunk of memory, not a 'C' string.
[#2] The memcpy function copies n characters from the object
pointed to by s2 into the object pointed to by s1. If
copying takes place between objects that overlap, the
behavior is undefined.
[#2] The memmove function copies n characters from the
object pointed to by s2 into the object pointed to by s1.
Copying takes place as if the n characters from the object
pointed to by s2 are first copied into a temporary array of
n characters that does not overlap the objects pointed to by
s1 and s2, and then the n characters from the temporary
array are copied into the object pointed to by s1.
Warner
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