Trouble with gpc_polygon_to_tristrip

[Zeotronic]

Recently I wrote code to convert my Box2D bodies' shapes into GPC polygons and tristrips. I decided rather than performing the operations to the tristrip as well, I would just convert the polygon into a tristrip... however, this has caused my game to crash on startup, with a "Segmentation Fault". Here is my code which is probably related to the crash, if you would like to help me but need more, let me know... though I personally think it unlikely there is a problem beyond this scope (as I have actually commented out all of the code related to tristrip rendering, and have the game working with out).

void PolygonDef_GPC(Body_Shape* bodyshape,b2PolygonDef* polydef,bool add=1){
long scan=0;
gpc_polygon shape;
gpc_polygon former;

//If bodyshape doesn't have a polygon
if (bodyshape->polygon==NULL)
{bodyshape->polygon=new gpc_polygon();}

//Copy bodyshape polygon
former=Copy_Polygon(*bodyshape->polygon);

//If bodyshape doesn't have a tristrip
if (bodyshape->tristrip==NULL)
{bodyshape->tristrip=new gpc_tristrip();}

//Prepare shape
shape.num_contours=1;
shape.hole=new int();
shape.hole[0]=0;
shape.contour=new gpc_vertex_list();
shape.contour[0].num_vertices=polydef->vertexCount;
shape.contour[0].vertex=(gpc_vertex*) malloc(shape.contour[0].num_vertices*sizeof(gpc_vertex));

//Write vertices to shape
while (scan<polydef->vertexCount){
shape.contour[0].vertex[scan].x=polydef->vertices[scan].x;
shape.contour[0].vertex[scan].y=polydef->vertices[scan].y;
scan++;
}

if (add){
//Add shape to shapes
gpc_polygon_clip(GPC_UNION,&former,&shape,bodyshape->polygon);
}
else {
//Remove shape from shapes
gpc_polygon_clip(GPC_XOR,&former,&shape,bodyshape->polygon);
}

//Copy Polygon to Tristrip
//gpc_polygon_to_tristrip(bodyshape->polygon,bodyshape->tristrip);
}
The last line, which is commented out, causes the crash when left in... I have used this before in different code, so I know that it can work... but I am clearly doing something wrong (unsuprising as I am new to GPC). So if you could tell me what I'm doing wrong?
I doubt you'll need knowledge of Box2D... just GPC.