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POCommon lisp, CFFI, and instantiating c structs
 

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  1. POCommon lisp, CFFI, and instantiating c structs
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    <p>I've been on google for about, oh, 3 hours looking for a solution to this "problem." I'm trying to figure out how to instantiate a C structure in lisp using CFFI. I have a struct in c:</p> <pre><code>struct cpVect{cpFloat x,y;} </code></pre> <p>Simple right? I have auto-generated CFFI bindings (swig, I think) to this struct:</p> <pre><code>(cffi:defcstruct #.(chipmunk-lispify "cpVect" 'classname) (#.(chipmunk-lispify "x" 'slotname) :double) (#.(chipmunk-lispify "y" 'slotname) :double)) </code></pre> <p>This generates a struct "VECT" with slots :X and :Y, which foreign-slot-names confirms (please note that I neither generated the bindings or programmed the C library (chipmunk physics), but the actual functions are being called from lisp just fine).</p> <p>I've searched far and wide, and maybe I've seen it 100 times and glossed over it, but I cannot figure out how to create a instance of cpVect in lisp to use in other functions.</p> <p>Note the function:</p> <pre><code>cpShape *cpPolyShapeNew(cpBody *body, int numVerts, cpVect *verts, cpVect offset) </code></pre> <p>Takes not only a cpVect, but also a pointer to a set of cpVects, which brings me to my second question: how do I create a pointer to a set of structs?</p> <p>I've been to <a href="http://common-lisp.net/project/cffi/manual/html_node/defcstruct.html" rel="nofollow">http://common-lisp.net/project/cffi/manual/html_node/defcstruct.html</a> and tried the code, but get "Error: Unbound variable: PTR" (I'm in Clozure CL), not to mention that looks to only return a pointer, not an instance.</p> <p>I'm new to lisp, been going pretty strong so far, but this is the first real problem I've hit that I can't figure out. Thanks!</p>
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    1. COallocate with FOREIGN-ALLOC?
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    2. COWorks for collections of pointers...half the problem. Thank you!!
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