[PD-dev] Using pd_bind and pd_findbyclass to access data from another external

[Miller Puckette]

That's indeed the difference - a c object like "send_test_class" can't
be shared beteen different object modules loaded separately into Pd.  This
is one reason people have sometimes put multiple externals into a single
object file.

You could have both externs have the same  "family name" (like
"array define" and "array set") - then they can both be defined in the
same C object file "binarytree.[extent]".

cheers
Miller

On Tue, Jan 19, 2021 at 11:38:22AM -0800, Eric Lennartson wrote:
> Hello all,
> 
> I've been working on trying to send data between different externals, but
> I'm not doing something quite right. I've looked at the code in d_global.c
> as well as for send and receive.
> The only difference I can see is that mine is not all in the same .c file
> while in the pd source it is.
> 
> Here's the external with the data. Just an int for now, but it will be
> holding a binary tree later.
> 
> static t_class *send_test_class;
> typedef struct _send_test {
>    t_object  x_obj;
>    t_symbol* name;
>    int value;
> }t_send_test;
> 
> static void *send_test_new(t_symbol *s, t_floatarg f) {
>    t_send_test *x = (t_send_test *)pd_new(send_test_class);
>    x->name = s;
>    x->value = f;
>    pd_bind(&x->x_obj.ob_pd, s); // bind to the name we're given
>    post("send_test created with name %s, and value %d", x->name->s_name,
> x->value);
>    return(x);
> }
> 
> static void send_test_free(t_send_test *x) {
>    pd_unbind(&x->x_obj.ob_pd, x->name); // unbind when deleted
> }
> 
> void send_test_setup(void) {
>    send_test_class = class_new(gensym("send_test"),
>                                  (t_newmethod)send_test_new,
>                                  (t_method)send_test_free,
>                                  sizeof(t_send_test),
>                                  CLASS_NOINLET,
>                                  A_DEFSYM,
>                                  A_DEFFLOAT,
>                                  0);
> }
> 
> And here's the receiver.
> 
> static t_class *send_test_class;
> 
> static t_class *rcv_test_class;
> 
> typedef struct _send_test {
>    t_object  x_obj;
>    t_symbol* name;
>    int value;
> }t_send_test;
> 
> typedef struct _rcv_test {
>    t_object  x_obj;
>    t_symbol* name;
> 
>    int value;
> } t_rcv_test;
> 
> static void *rcv_test_new(t_symbol *s) {
>    t_rcv_test *x = (t_rcv_test *)pd_new(rcv_test_class);
>    x->name = s;
>    t_send_test* sender = (t_send_test*)pd_findbyclass(x->name,
> send_test_class);
> 
>     x->value = sender->value;
>     post("sender value is %d", sender->value);
>     post("rcv_test created with name %s, and value %d", x->name->s_name,
> x->value);
>     return(x);
> }
> 
> static void rcv_test_free(t_rcv_test *x) {}
> 
> void rcv_test_setup(void) {
>    rcv_test_class = class_new(gensym("rcv_test"),
>                                                (t_newmethod)rcv_test_new,
>                                                (t_method)rcv_test_free,
>                                                 sizeof(t_rcv_test),
>                                                 CLASS_NOINLET,
>                                                 A_DEFSYM,
> 
>                                                 0);
> }
> 
> What exactly is it that I'm doing wrong?

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