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From: jima@hplsla.HP.COM (Jim Adcock)
Newsgroups: comp.lang.c++
Subject: Re: calculate member byte offset
Message-ID: <6590284@hplsla.HP.COM>
Date: 6 Oct 89 18:58:01 GMT
References: <1989Oct5.193826.24178@polyslo.CalPoly.EDU>
Organization: HP Lake Stevens, WA
Lines: 25

>//Thomas Wang
>//I need to know the byte offset of 'header' in class 'foo' before any
>//'foo' object is allocated.

class foo
{
public:
  int grr;
  int header;		//does header stuff really need to be public?
  void alloc();
};

void foo::alloc()
{
  cout << (&(this->header)) - this << "\n";   // bomb! 2.0 complains that this
// is of type foo*, while &(this->header) is of type int*.  Maybe you can get
// away with coercing them both to type char*, but not guaranteed to work with
// all compilers
}

main()
{
  ((foo*) 0) -> alloc();   // bomb?  -- possible on a machine that
		  	   // disallows dereferencing a null pointer
}