double pointer to function

[Chris Torek]

In article <107 at cyclopes.UUCP> stergios at athsys.uucp (Stergios Marinopoulos)
writes:
>Can anyone figure out why the following code does not compile
>correctly?  The first ?/: pair makes cc (sun 3.4) complain ....
>[(This is] the ouput of a C++ translator [).]

Sun's compiler is correct to complain.  Retaining only the relevant
code, and deleting various unnecessary parentheses:

>struct A { int (**A_tablePtr)(); };
>  struct A *this ;
>  void *pmf ;
>  extern int flag ;
>  flag ? *(void (**)())pmf :
>	  this->A_tablePtr[(unsigned int)*(void (**)())pmf) - 1]

Examine the types of the objects on each side of the `:':

	*(void (**)())pmf   =>
	    cast pmf to
		pointer to pointer to function returning void
	    then indirect, so type is
		pointer to function returning void

	this->A_tablePtr[ <horrible unsigned-int-valued expression> ]   =>
	    subscript (indirect) an object of type
		pointer to pointer to function returning int
	    so type is
		pointer to function returning int

Both are pointers to functions, but one returns void, the other int.
For the expressions to be compatible, either the ?: line must read

	flag ? *(int (**)())pmf : <original rhs>

or the delcaration of `struct A' must read

	struct A { void (**A_tablePtr)(); };
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7163)
Domain:	chris at mimsy.umd.edu	Path:	uunet!mimsy!chris