Re: Avoiding _memset?

"Ben Voigt [C++ MVP]" <bvoigt@newsgroup.nospam>
Tue, 8 Sep 2009 15:01:40 -0500
"Vincent Fatica" <> wrote in message

(VC9) I am trying to avoid the runtime library in a tiny app (something I
regularly). When I try to zero-fill a STARTUPINFO struct with a for-loop,
compiler turns my for-loop into a call to _memset.

; 13 : STARTUPINFO si;
; 14 : si.cb = sizeof(si);
; 15 : for (BYTE *p = (BYTE*) &si + sizeof(si.cb); p < (BYTE*) &si +
sizeof(si); p++)
; 16 : *p=0;

push 64 ; 00000040H
lea edx, DWORD PTR _si$[esp+104]
push 0
push edx
add esi, 2
mov DWORD PTR _si$[esp+108], 68 ; 00000044H
call _memset
add esp, 12 ; 0000000cH

How do I avoid that (elegantly)? Is it some kind of optimization I can
turn off? I can trick the compiler with the likes of

; 16 : *p = p ? 0 : 1; // in the loop

That avoids the _memset, but seems particularly kludgy.

You can use the ZeroMemory macro, which results in a call to ntdll.dll's
RtlZeroMemory routine instead of pulling in the CRT.

- Vince

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