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From: waldemar@mit-vax.LCS.MIT.EDU (Waldemar Horwat)
Newsgroups: comp.lang.c++
Subject: Type Compatibility
Message-ID: <5485@mit-vax.LCS.MIT.EDU>
Date: 20 Jan 89 22:53:17 GMT
Organization: MIT LCS, Cambridge, MA
Lines: 42

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Reply-To: waldemar@mit-vax.UUCP (Waldemar Horwat)
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Organization: MIT Laboratory for Computer Science, Cambridge
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Given the declarations below, which of the following seven statements
(numbered 1, 2, 4, 5, 6, 7, and 8) are acceptable in a "portable" C++ program?
Specifically, I am trying to clarify the following issue:
  If a pointer to B can be passed to a function that takes a pointer to A,
  then can a pointer to a pointer to B be passed to a function that takes a
  pointer to a pointer to A?  What if A is void?
I'd also be interested in hearing what real compilers do with the following
code.
struct A {int x;};
struct B:A {int y;};

extern void f1(void *);
extern void g1(A *);
extern void i1(A &);

extern void f2(void **);
extern void g2(A **);
extern void h2(void *&);
extern void i2(A *&);

B b,*pb,**ppb;

void test()
  {
  f1(pb);   //1
  g1(pb);   //2
  i1(b);    //4
  
  f2(ppb);  //5
  g2(ppb);  //6
  h2(pb);   //7
  i2(pb);   //8
  }

				Waldemar Horwat
		      Internet: waldemar@vx.lcs.mit.edu