OpenEuphoria

Re: Structures

• Posted by "Cuny, David at DSS" <David.Cuny at DSS.CA.GOV> Feb 02, 2000
• 584 views

Everett Williams wrote:

> Cheapshot!

Yes. I couldn't resist, but I should have.

Let me see if I understand what you are asking for. The Real World
implements things using C structures. Calls to external DLLs, reading binary
data - all of these deal with data in a C structure, which then has to be
laboriously mapped to and from Euphoria data.

If I understand you, you are suggesting that it would be nice if you could
link Euphoria variables to C structures. For example, given a structure like
this:

   struct point
      integer x as C_INT
      integer y as C_INT
   end struct

You could then declare an instance of the structure:

   point myPoint

and assign data to the structure:

   myPoint.x = 12
   myPoint.y = -3

fetch data from the structure:

   ? myPoint.x

pass the data structure or elements to DLLs:

   result = c_func( DLL_FUNC, { *myPoint } )

   result = c_func( DLL_FUNC( { *myPoint.x } }

and peek/poke/perform memory moves:

   poke( hMemoryAddress, *myPoint, sizeof( myPoint ) )

Note that I've had to prefix the structure and structure element with a '*',
so Euphoria knows I want the address, and not the value of the structure or
structure element.

Am I (more or less) correct here?

To some extent, Win32Lib already has tools to do this sort of thing. For
example, I can declare a structure:

   constant POINT
      POINT_X = allot( Integer ),
      POINT_Y = allot( Integer )
      SIZEOF_POINT = allotted_size()

I can create the structure in memory:

   atom hPoint
   hPoint = allocate_struct( SIZEOF_POINT )

assign values:

   store( hPoint, POINT_X, 12 )
   store( hPoint, POINT_Y, -3 )

fetch the values:

   ? fetch( hPoint, POINT_X )

pass them to functions:

   result = c_func( C_FUNC, { hPoint } )

It deals transparently with a number of data types, include lpzString. It's
a fairly close mapping to C structures, and works fairly well. It's missing:

   embedded structure support
   arrays of structures

But these aren't too hard to simulate, and if I really need them, I can
always add them in. It's not as *nice* as working with native Euphoria, but
it's worked well for me.

-- David Cuny