FFI kick start

FFI kick start

[john]

Hi guilers...

I am trying to get to grips with manually wrapping C functions but
need some pointers. I have a C function:

packedEncode *initializeEncode(char *pdu, int size)

with:

typedef struct {
  char *pdu;
  ...

} packedEncode;

It takes a pointer to some storage (char *pdu) which will be mutated
by other wrapped C functions and finally retrieved. I am running into
segfault problems when it comes to mutating the data from C and then
trying to access it. I would really appreciate some pointers or some
boiler plate code for handling this type of function to get me
rolling.

TIA,

John.

Re: FFI kick start

[Linas Vepstas]

2008/10/14 john <jptmoore@gmail.com>:
> Hi guilers...
>
> I would really appreciate some pointers or some
> boiler plate code for handling this type of function to get me
> rolling.

I found that
http://www.gnu.org/software/guile/manual/html_node/The-Complete-Example.html

was enough to get me going.

Alternately, take a look at the source code for "gnotime";
it wraps a bunch of OO-style objects in a simple way,
with just a small amount of guile code.

--linas

Re: FFI kick start

[Andy Wingo]

On Tue 14 Oct 2008 11:43, john <jptmoore@gmail.com> writes:

> I am trying to get to grips with manually wrapping C functions but
> need some pointers. I have a C function:
>
> packedEncode *initializeEncode(char *pdu, int size)

You need to create a smob type for the packedEncode data structure. Make
sure that if C has a reference to it, that Scheme does also. Check the
section of the manual about "SMOBs".

Andy
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