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

David Wilkinson <>
Thu, 03 Dec 2009 10:25:00 -0500
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.

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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