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Re: Passing C pointers through guile

From: Ludovic Courtès
Subject: Re: Passing C pointers through guile
Date: Sat, 05 Jul 2008 18:59:26 +0200
User-agent: Gnus/5.11 (Gnus v5.11) Emacs/22.2 (gnu/linux)


"Maciek Godek" <address@hidden> writes:

> is there any portable and recommended way for passing C pointers around
> in guile environment?
> I think of something like scm_to_ptr (analogous to scm_to_int etc.).
> Certainly such a value would be completely useless for the interpreter.
> One can achieve simillar functionality using the aforementioned
> scm_to_int (keeping track on the word length of the build target),
> but it seems rather unnatural.

If the goal is to make a C object pointed to by some pointer available
to Scheme functions, the recommended (and simplest) way is to use a
"SMOB" (see the manual for details).  In practice, SMOBs incur some
storage overhead because they hold 4 machines words, while you may only
need one.

Another possibility is to use a "uo" field in a struct: it allows you to
have a struct field holding a machine word inaccessible to Scheme
functions (see the "Vtables" node of the manual).

Hope this helps,

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