Re: Ada equivalent for C-pointer?

[Duncan Sands <baldrick@free.fr>]

Hi Alfred,

> I want to interface to a C-function expecting a "far *", what have I to
> pass: an "access all ..." or "System.Address"? Are there differences
> between access and address, or are their internal representations equal?
> I use GNAT 3.15p.

a System.Address is what you would expect a pointer to be: a (eg) 32 bit
number referring to a memory address, like a C pointer.  Most access types
will be the same size as, and equivalent to, a System.Address, but some
access types may be bigger ("fat pointers") because they contain some
information about what they are pointing to.  This is typical of access
to unconstrained array types for example, where the access type usually
holds a memory address and also the array bounds.  What you should do is
create an access type with convention C:

	type C_Pointer is access ...
	pragma Convention (C, C_Pointer);

Here ... is whatever it is your pointer is pointing to, or anything (eg: Integer)
if you are not actually going to dereference the pointer in your Ada program.  The
pragma makes sure that the access type is what a C program expects, basically a
System.Address.

Ciao,

Duncan.