OpenEuphoria

Re: vMac

• Posted by Robert Craig <rds at EMAIL.MSN.COM> Oct 07, 1998
• 492 views

Robert Craig wrote:
>In C, you can't code a call to a routine when you
>don't know until run-time how many arguments to pass *or*
>what type those arguments are.
Hawke' replied:
> why is it that for the function parameters in this situation,
> you cannot simply have a single pointer as your parameter,
> and have that single pointer paramenter at runtime point
> to an array of pointers to where each pointer at each array
> element was a pointer to a parameter you wanted to pass?

Your solution is fine if you are the one writing both the
subroutine and the calls to it.

The problem in exw is that I have to set up a call to an
*arbitrary* C routine in a .DLL.  The C routine was written by
someone else and it expects to receive a certain number of
arguments on the stack, each with a specific type such as
int, double, etc. If it isn't done correctly then the program will
likely crash.

Your Euphoria program tells exw at run-time what the
arguments to the C routine should be (see define_c_func()).
When you later call c_func(), exw has to set up the call stack
in the way that's expected by a WIN32 API call with that many
arguments of those types. The call stack is not something that you can
play with directly through C. You have to use a bit of
assembly code to manipulate it (the PUSH instruction for instance).

To the WATCOM C compiler it looks like I'm making a simple
call via a function pointer to a 0-argument C function. In fact, I've
already pushed your various arguments of various types onto the
call-stack via some assembly code, and magically it all works.
(Of course I crashed my machine numerous times trying to debug
this stuff.)

Regards,
     Rob Craig
     Rapid Deployment Software
     http://members.aol.com/FilesEu/