Messages in this thread | | | Subject | Re: [PATCH] Repalce strncmp by memcmp | From | YOSHIFUJI Hideaki <> | Date | Mon, 29 Nov 2010 14:26:02 +0900 |
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2010-11-28 (Sun) 20:13 -0800, Dmitry Torokhov wrote: > On Mon, Nov 29, 2010 at 06:11:21AM +0300, Pavel Vasilyev wrote: > > On 29.11.2010 05:29, Ming Lei wrote: > > > Hi, > > > > > > 2010/11/29 Pavel Vasilyev <pavel@pavlinux.ru>: > > >> This patch replace all strncmp(a, b, c) by memcmp(a, b, c). > > >> > > >> I test on x86_64 (AMD Opteron 285). > > > In fact, memcmp doesn't handle case of tail of string, so > > > it is not safe to replace strncmp with memcmp > > > > > #include <stdio.h> > > #include <errno.h> > > > > int main() { > > > > char *STR = "XXXX\0"; > > char *XXX = "XXXX"; > > Try comparing: > > "XXXX\0YYYY" and > "XXXX\0ZZZZ" > > and observe the difference. >
Yes, if both of the strings are NOT known to have enough length.
It is safe to replace strncmp(a,b,n) with memcmp(a,b,n) if a or b is/are known to have enough length; strlen(a) >= n || strlen(b) >= n.
I think some of the replacements in the original patch are valid, but for even those valid replacement, I think it is worth doing that in hot code paths only.
--yoshfuji
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