Re: Type cast problem with VC++ 2005 Express Edition

From:
"aslan" <aslanski2002@yahoo.com>
Newsgroups:
microsoft.public.vc.language
Date:
Thu, 3 Dec 2009 17:41:09 +0200
Message-ID:
<eFXpL8CdKHA.2160@TK2MSFTNGP02.phx.gbl>
"David Wilkinson" <no-reply@effisols.com>, iletisinde ??unu yazd??,
news:%23UmhHzCdKHA.2160@TK2MSFTNGP02.phx.gbl...

aslan wrote:

OK I tried something else.

struct bool_struct
{
  bool a[32];
};
int main(int argc, char**argv)
{
  bool_struct* p=new bool_struct;
  return 0;
}

so "new bool_struct" ends up by calling the following cb=32.

void * operator new( unsigned int cb )
{
   void *res = _nh_malloc( cb, 1 );

   return res;
}

So 32 byte is allocated for "bool a[32];"

Also the following quote from MSDN help installed with VC++ 6 which
confirms the size of 1 byte for VC++ 6;

Microsoft Specific

In Visual C++4.2, the Standard C++ header files contained a typedef that
equated bool with int. In Visual C++ 5.0 and later, bool is implemented
as a built-in type with a size of 1 byte. That means that for Visual C++
4.2, a call of sizeof(bool) yields 4, while in Visual C++ 5.0 and later,
the same call yields 1. This can cause memory corruption problems if you
have defined structure members of type bool in Visual C++ 4.2 and are
mixing object files (OBJ) and/or DLLs built with the 4.2 and 5.0 or later
compilers.

END Microsoft Specific


All this is about the bool type. In VC6 and beyond, sieof(bool) is 1.

OK. Tim Roberts was talking about MS STL implementation whereas I use SGI
STL implementation so I didn't notice it then.

The complication is that vector<bool> is not always implemented in the
straightforward way that it is for other types. Though it should be, IMHO.

--
David Wilkinson
Visual C++ MVP

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