Re: pragma convention

["Jeffrey R. Carter" <spam@spam.com>]

Anonymous Coward wrote:

> You raise a good point, assuming C compilers all have the freedom to
> represent types arbitrarily.  So what's the point of the current
> existence of pragma Convention?  What can I expect pragma convention
> to do for me?

pragma Convention (X, ...

really means the convention used by some specific X compiler chosen by the Ada 
compiler developers for those cases where the X language does not rigorously 
specify the characteristic in question.

Convention C does do certain common things for you. For an access type, you 
insure that it is just a pointer, and doesn't contain any additional data (which 
Ada's access values can and sometimes do contain). For subprograms, you get 
automatic conversion of parameters to pointers to match C passing rules and make 
[in] out parameters work properly.

This latter is very useful; you can write

procedure C (X : out Interfaces.C.Int);
pragma Import (C, X, "xInC");

and the compiler takes care of passing a pointer for you.

-- 
Jeff Carter
"Perfidious English mouse-dropping hoarders."
Monty Python & the Holy Grail
10