OpenEuphoria

Re: Accessing C variables/structures

• Posted by Matthew Lewis <MatthewL at KAPCOUSA.COM> Jul 26, 2000
• 430 views

> -----Original Message-----
> From: Ben Logan

> When using a C library from Euphoria, how do I access the
> variables and
> structures made available by that library?

As Bernie mentioned, this only works with DLL's, like the win32 API.

I'd recommend checking out win32lib's handling of structures.  The important
routines are:

allot()
allocate_structure()
allotted_size()
fetch()
store()

Basically, you define a series of constants that you'll use to access
structures.  For example, if the C declaration looks somthing like:

typedef struct _point{
LONG    rectLeft;
LONG rectTop;
LONG rectRight;
LONG rectBottom
} POINT;

Then in Eu you'd do this:

global constant
    rectLeft            = /allot( Long ),
    rectTop             = /allot( Long ),
    rectRight           = /allot( Long ),
    rectBottom          = /allot( Long ),
    SIZEOF_RECT        = /allotted_size()

When you want to create a RECT structure yourself:

atom rect

rect = allocate_struct( SIZEOF_RECT )

store( rect, rectLeft, left )
store( rect, rectTop, top )
store( rect, rectRight, right )
store( rect, rectBottom, bottom )

To retrieve values, you simply use fetch:

left = fetch( rect, rectLeft )
etc...

C functions will return pointers to structures.  So if you receive a pointer
to a RECT structure, just substitute that value for 'rect' above.  It's
important to remember to use free() when you're done with a structure, so
you don't leak memory.  Also, if the structure includes a pointer to a
string (usually starts with 'lpsz') you'll need to free_strings() when
you're done with it.

Matt