Thanks to Han's help page (http://puredata.info/docs/developer/mingw) I was able to compile a test external on windows with mingw.

I then started making a new external called getdollarzero based on getdir (from ggee) and parentdollarzero (from iemlib2). I compiled it and it works but I had to:
1) remove Guenter's hack from getdir's source code
2) and therefore include g_canvas.h

My question is the following: why is there a hack in the first place? If I do not use it will my code crash PD in some way (I compiled against PD 0.4 and worked fine during testing)?

As a reference, here is my code with the hack commented out :

--------- getdollarzero --------

#include "m_pd.h"
#include "g_canvas.h" //needed to include g_canvas.h once the hack was commented out

/* HACK
struct _glist
{
    t_object gl_obj;            // header in case we're a glist
    t_gobj *gl_list;            // the actual data
    struct _gstub *gl_stub;     // safe pointer handler
    int gl_valid;               // incremented when pointers might be stale
    struct _glist *gl_owner;    // parent glist, supercanvas, or 0 if none
};

END HACK
*/

typedef struct getdollarzero
{
    t_object x_ob;
    t_canvas * x_canvas;
    t_outlet* x_outlet;
    int x_level;
} t_getdollarzero;

static void getdollarzero_bang(t_getdollarzero *x)
{
    int i = x->x_level;
    t_canvas* last = x->x_canvas;

    while (i>0) {
        i--;
        if (last->gl_owner) last = last->gl_owner;
    }
// code example taken from iemlib2's parentdollarzero:
    // x->s_parent_unique = canvas_realizedollar((t_canvas *)this_canvas->gl_owner, gensym("$0"));
    // original get dir function:
    //outlet_symbol(x->x_outlet,canvas_getdir(last));

    outlet_symbol(x->x_outlet,canvas_realizedollar(last, gensym("$0")));
}

t_class *getdollarzero_class;

static void *getdollarzero_new(t_floatarg level)
{
    t_getdollarzero *x = (t_getdollarzero *)pd_new(getdollarzero_class);
    x->x_canvas = canvas_getcurrent();
    x->x_outlet = outlet_new(&x->x_ob, &s_);
    x->x_level = level;
    return (void *)x;
}

void getdollarzero_setup(void)
{
    getdollarzero_class = class_new(gensym("getdollarzero"), (t_newmethod)getdollarzero_new, 0,
        sizeof(t_getdollarzero), 0, A_DEFFLOAT,0);
    class_addbang(getdollarzero_class, getdollarzero_bang);
}

--------- getdollarzero end --------

--
thomas ouellet fredericks, tof@danslchamp.org, montreal, canada