Interfacing to void *

[William Starner <billeug@worldnet.att.net>]

If I'm trying to interface to a C library that uses this struct

struct BigNum {
	void *ptr;
	unsigned int size;
	unsigned int allocated;
};

how should I interface to void*?

I have
private
	type voidpointer is access character;
	type BigNum is record 
		ptr: voidpointer;
		size: Interfaces.C.unsigned;
		allocated: Interfaces.C.unsigned;
	end record;
	type RealBigNum is access BigNum;
	type UnboundedInt is new Linear with record
		Value: RealBigNum;
	end record;
end nla23.linear.bnlib;
but char* = void* is a C rule, not an Ada rule. It probably works, but it's not
right. (I don't need to access anything through that pointer.)