OpenEuphoria

Re: call_back ?

• Posted by Don <eunexus at yahoo.com> Jul 24, 2004
• 492 views

> Can EU not do this?
> ... specifically, this definition for a user defined API 'function' says, *NO*
> return
> value.
> 
> VOID WINAPI RasDialFunc(
> 
>     UINT unMsg, // type of event that has occurred
>     RASCONNSTATE rasconnstate, // connection state about to be entered
>     DWORD dwError // error that may have occurred
>    ); 
> 
>  Return Values
> None.
> 
> .. anyways, it's 'puking' all over me, so I'm.. just wondering, how ??

Actually this doesnt matter one bit as far as EU is concerned.  Or any
other language.

Under all the sugar of high/ mid level languages (even C) you can see
from looking at assembly code whats actually happening...

1> you call a function
2> the return value is placed into register EAX (or not)
3>
     A> if you need the return value you can assign it to a variable from EAX
     B> if you dont need it just dont do anything and EAX just sits there

Everything else doesnt matter.  If you assign a return value from a
function call you are getting the contents of the EAX register.  If you
dont need it thats fine.  The value is *still* in the EAX register.
In other words functions with and without return values are coded
the exact same way.

If they are coded the same way (which they are), you can go ahead
and use your call as a function that *does* return a value.  And you
can even assign the return to a variable (which in EU is required).
Just realise that the value returned will have no meaning because,
if they were nice, they zeroed EAX before returning.  Its possible
they did not touch it however and it would contain whatever just happens
to be there before the call happened...


Don Phillips - aka Graebel
     National Instruments
     mailto: eunexus @ yahoo.com