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From: xmllmx <xmllmx@gmail.com>
Newsgroups: comp.os.ms-windows.programmer.nt.kernel-mode
Subject: Re: Is memcmp an unsolved symbol in NT kernel driver even if compiled with /Oi?
Date: Sat, 26 May 2012 13:37:11 -0700 (PDT)
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On Sunday, May 27, 2012 4:19:07 AM UTC+8, Don Burn wrote:
> Use RtlCompareMemory not memcmp.
> 
> 
> Don Burn
> Windows Filesystem and Driver Consulting
> Website: http://www.windrvr.com
> Blog: http://msmvps.com/blogs/WinDrvr
> 
> 
> 
> 
> "xmllmx" <xmllmx@gmail.com> wrote in message 
> news:44201cc4-e49a-49fe-9335-5f642e911afd@googlegroups.com:
> 
> > Code Sample 1:
> >
> > #include <ntifs.h>
> >
> > NTSTATUS DriverEntry(PDRIVER_OBJECT param1, PUNICODE_STRING param2)
> > {
> > 	char s1[] = "Hello";
> > 	char s2[] = "World";
> >
> > 	int n = memcmp(s1, s2, 5);
> >
> > 	return 0;
> > }
> >
> > WDK compiler reports: error LNK2019: unsolved extern symbol _memcmp referenced in function _DriverEntry@8
> >
> > However, if I modify a bit the code as follows, then the compiler will accept it.
> >
> > Code Sample 2:
> >
> > #include <ntifs.h>
> >
> > NTSTATUS DriverEntry(PDRIVER_OBJECT param1, PUNICODE_STRING param2)
> > {
> > 	char s1[] = "Hello";
> > 	char s2[] = "World";
> >
> > 	memcmp(s1, s2, 5);
> >
> > 	return 0;
> > }
> >
> > Why?
> >
> > Thanks in advance!

Dear Don,

I know RtlCompareMemory is a better choice. But I just wonder its cause. I have a third-party source code which uses a lot of memcmp, so I have to solve it. 

Thank you very much.