"void **" : Is it valid and what does it mean?

[Georg Wittig]

hp at vmars.tuwien.ac.at (Peter Holzer) writes:

>[...good explanation why void ** isn't a pointer to any pointer

>>Why do you want to do _that_?

>For some reason, which is not relevant here, msg is not a pointer to
>the structure, but a pointer to a pointer to structure. Of course one
>common error is to define a struct foo * mymsg and then pass mymsg
>instead of &mymsg. With the current prototype this error is not
>detected by the compiler, but if some type `pointer to any pointer'
>existed, this type of error could be catched. Unfortunately this is not
>possible in C.

Why not use unions? Example:

	typedef union {	struct struct1 *p_struct1;
			struct struct2 *p_struct2;
			...
		      } my_union_t;

and pass the union address to your function:

	myfunc (&myunion);
	...
	myfunc (my_union_t *p_union){
		...
		p_union -> p_struct2 -> ...

This has the advantage that you MUST define which structures are allowed in
that context, and the compiler can check consistency. ... And you don't
need void **.
-- 
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