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Re- A C pointer passed to LISP

To:   Sheldon Shen,   shen@dolphin.Jpl.Nasa.Gov
cc:   info-mcl
From: Steve Mitchell
Date: 02-11-92
Sub:  A C pointer passed to LISP
> In my program, I pass a C pointer to LISP. It is a pointer to a
> STRUCT that maintains the status of a database.
> Eval (zone-pointer my-pointer) returns NIL. I guess it means that
> this is a relocatable pointer.
Not at all; your struct may be allocated on the stack. And take
note that the docs for zone-pointerp make it clear that it is the
memory block, not the pointer, that may or may not be relocatable.
> Repeatedly updating the database (or repeatedly using this pointer)
> eventually crashes the system.
It doesn't sound like you're actually getting your pointer into MCL.
Perhaps the argument type, order, or argument-passing method is not
specified correctly in your interface definition.
> Is there anyway to force a relocatable pointer non-relocatable?
Pointers point to non-relocatable heap storage. #_NewHandle
allocates a relocatable heap block and returns a HANDLE to it. You
can call #_HLock on the handle to make its block non-relocatable.