C Integers -> Booleans: shortcut?

C Integers -> Booleans: shortcut?

[chris]

Hi,

Can you (in general) import a function taking/returning a C integer and 
treat it like a boolean for import?  Let the compiler deal with the 
difference?

Like say,

function is_broke (something : sometype) return Boolean;


pragma Import (C, Is_Broke, "is_broke");

with is_broke actually,

int is_broke (sometype something);


instead of going through

function is_broke (something : sometype) return Boolean is
begin
    return c_is_broke (something) /= 0;
end is_broke;


Cheers,
Chris

Re: C Integers -> Booleans: shortcut?

[Simon Wright]

chris <spamoff.danx@ntlworld.com> writes:

> Can you (in general) import a function taking/returning a C integer
> and treat it like a boolean for import?  Let the compiler deal with
> the difference?

With GNAT you would say

  type C_Boolean is new Boolean;
  pragma Convention (C, C_Boolean);

with the meaning that 0 => False, anything else => True.

For other compilers I would think you'd be better off specifying
Interfaces.C.int and comparing to 0.

Re: C Integers -> Booleans: shortcut?

[chris]

Simon Wright wrote:

> With GNAT you would say
> 
>   type C_Boolean is new Boolean;
>   pragma Convention (C, C_Boolean);
> 
> with the meaning that 0 => False, anything else => True.

I thought GNAT would do that, but hoped other compilers would too since 
it's the convention in C for 0 to be treated like false and anything 
else as true.

> For other compilers I would think you'd be better off specifying
> Interfaces.C.int and comparing to 0.

Will do! Thanks!

Re: C Integers -> Booleans: shortcut?

[Randy Brukardt]

"Simon Wright" <simon@pushface.org> wrote in message
news:x7vpthkrg0h.fsf@smaug.pushface.org...
> chris <spamoff.danx@ntlworld.com> writes:
>
> > Can you (in general) import a function taking/returning a C integer
> > and treat it like a boolean for import?  Let the compiler deal with
> > the difference?
>
> With GNAT you would say
>
>   type C_Boolean is new Boolean;
>   pragma Convention (C, C_Boolean);
>
> with the meaning that 0 => False, anything else => True.
>
> For other compilers I would think you'd be better off specifying
> Interfaces.C.int and comparing to 0.

Janus/Ada automatically converts Boolean to the C equivalent for calls. We
used it in our early Windows bindings - made things quite a bit clearer.

But the point is that it isn't standard, so if you want your code to work on
other compilers, don't do that. Claw doesn't use that, for instance.

                   Randy.