Re: Why I don't use the " /O2 " compiler option.

From:

"Alexander Grigoriev" <alegr@earthlink.net>

Newsgroups:

microsoft.public.vc.language

Date:

Thu, 6 Dec 2007 06:04:50 -0800

Message-ID:

<eKpJEFBOIHA.4440@TK2MSFTNGP06.phx.gbl>

Why do you expect anything different from printing Int64?

Again, there is no 8 bytes alignment guarantee in MS VC 32 bit. Each stack
frame can take multiple of 4 bytes, not 8 bytes.

"Jeff?Relf" <Jeff_Relf@Yahoo.COM> wrote in message
news:Jeff_Relf_2007_Dec_5__1_29_Pw@Cotse.NET...

Given VC++ 8, a 32 bit CPU,
the " /O2 " compiler option ( to Optimize for Speed )
and this code:

" #include <Windows.H>
#include <StdIO.H>

   #pragma warning( disable: 4996 )
int _stdcall WinMain( HINSTANCE, HINSTANCE, char*, int ) {
   __int64 Int64 = 0xCCCCCCCCCCCCCCCC ;
   FILE * fp = fopen( "AA.TXT", "w" );
   fprintf(
       fp, "%p, %d, %I64X", & Int64, int( & Int64 ) % 8, Int64 );
   fclose( fp ); // * ( __int64 * ) ( ( char * )& Int64 + 4 )
   // Now, AA.TXT has: ' 0012FF04, 4, CCCCCCCCCCCCCCCC '.
} ",

8-byte integers are not 8-byte-aligned. Worse,
the debugger lies about both the contents of Int64 and its address.

When debugging,
" * ( __int64 * ) ( ( char * ) & Int64 + 4 ) " is the true address.

Now you know why I don't use the " /O2 " compiler option.