[plt-scheme] foreign: am I missing something basic?

From: Dave Herman (dherman at ccs.neu.edu)
Date: Sun Sep 27 16:51:58 EDT 2009

Hm, I don't know. I've written DLL's in Visual Studio for use with  
scheme/foreign before, and never had these problems. However, I don't  
think I ever passed arbitrary Scheme objects; the API's I used were  
just passing simple primitives that scheme/foreign translates  
automatically to corresponding C types. I suppose it's possible I've  
been building the DLL's wrong all along. But I'm not sure what I would  
need to change to fix such an issue.

Just a couple more data points:

* I made sure the program is being compiled as C and not C++, but to  
be sure I added a __cdecl modifier to the function declaration, with  
no difference in behavior.

* I have tried debugging the crashed DLL in Visual Studio, and it's  
showing the value of the pointer x as the very suspicious value 0x95;  
the crash is an access violation (can't read from that protected  

* The syntax object doesn't seem to be the main culprit; when I pass a  
pair to peek-inside, the value of x is 0x65 and again the DLL crashes  
with an access violation.


On Sep 27, 2009, at 7:59 AM, Noel Welsh wrote:

> On Thu, Sep 24, 2009 at 3:15 AM, Dave Herman <dherman at ccs.neu.edu>  
> wrote:
>>    (define peek-inside
>>      (get-ffi-obj 'peek_inside lib (_cprocedure (list _scheme)  
>> _short)))
> An idiomatic definition would be:
> (_fun _scheme -> _short)
> instead of your _cprocedure definition.
> Perhaps the issue is one of calling conventions?  I know Windows uses
> the "Pascal" (stdcall?) calling convention for it's libraries. Perhaps
> shared libraries are automatically defined with this convention?
> N.

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