Olaf Matthes

I hope this is a stupid question (because I already stared at all this 

code for too long): how do I access the return value of a 

object_method() call in an obex external?

The pattr SDK docs state: "If the receiver object can respond to the 

message, object_method returns the result. Otherwise, the function will 

The function I'm calling is supposed to return a double, the code I got 

retval = (double *)object_method(x->x_childobj, gensym("doit"), array);

But as soon as I try to access the retval (even checking whether it's == 

NULL) Max crashes. (Windows XP, latest Max, latest SDK, VC++ 6.0.)

I can't use object_method_typed() here because I have to pass my 

function a float** array that won't fit into a t_atom. On a similar 

function call (that also crashed) the use of object_method_typed() 

solved the problem of getting the return value.

And a related question: would it hurt if I call the function directly 

(without using the object_method... call)? At least it doesn't crash 

this way. - I really don't like the idea of putting my float** into a 

I hope this is a stupid question (because I already stared at all this 
code for too long): how do I access the return value of a 
object_method() call in an obex external?

The pattr SDK docs state: "If the receiver object can respond to the 
message, object_method returns the result. Otherwise, the function will 
return 0."

The function I'm calling is supposed to return a double, the code I got 
to compile look slike this:

retval = (double *)object_method(x->x_childobj, gensym("doit"), array);
if (*retval != NULL)
    post("do something with it");

But as soon as I try to access the retval (even checking whether it's == 
NULL) Max crashes. (Windows XP, latest Max, latest SDK, VC++ 6.0.)

I can't use object_method_typed() here because I have to pass my 
function a float** array that won't fit into a t_atom. On a similar 
function call (that also crashed) the use of object_method_typed() 
solved the problem of getting the return value.

And a related question: would it hurt if I call the function directly 
(without using the object_method... call)? At least it doesn't crash 
this way. - I really don't like the idea of putting my float** into a 
hughe amount of t_atoms...

obex-how-to-get-return-values-from-object_method

On Jun 29, 2006, at 1:31 PM, Olaf Matthes wrote:

> I hope this is a stupid question (because I already stared at all 

> this code for too long): how do I access the return value of a 

> object_method() call in an obex external?

> The pattr SDK docs state: "If the receiver object can respond to 

> the message, object_method returns the result. Otherwise, the 

> The function I'm calling is supposed to return a double, the code I 

> retval = (double *)object_method(x->x_childobj, gensym("doit"), 

> But as soon as I try to access the retval (even checking whether 

> it's == NULL) Max crashes. (Windows XP, latest Max, latest SDK, VC+ 

You can't use a pointer to grab a double as above (unless you 

actually return a double pointer, which will remain valid beyond the 

extent of the function called). So, you'll need to create a double 

return value prototype like the following:

typedef double (* t_double_method)(void *, ...);

Then get the method pointer with zgetfn or class_getmethod()

Sorry, if there are typos, as I'm writing this quickly in an airport, 

> I hope this is a stupid question (because I already stared at all  
> this code for too long): how do I access the return value of a  
> object_method() call in an obex external?
>
> The pattr SDK docs state: "If the receiver object can respond to  
> the message, object_method returns the result. Otherwise, the  
> function will return 0."
>
> The function I'm calling is supposed to return a double, the code I  
> got to compile look slike this:
>
> double *retval = NULL;
>
> retval = (double *)object_method(x->x_childobj, gensym("doit"),  
> array);
> if (*retval != NULL)
>    post("do something with it");
>
> But as soon as I try to access the retval (even checking whether  
> it's == NULL) Max crashes. (Windows XP, latest Max, latest SDK, VC+ 
> + 6.0.)

You can't use a pointer to grab a double as above (unless you  
actually return a double pointer, which will remain valid beyond the  
extent of the function called). So, you'll need to create a double  
return value prototype like the following:

double retval;
retval = myfn(x->x_childobj, array);

Sorry, if there are typos, as I'm writing this quickly in an airport,  
but this should give you an idea.

> You can't use a pointer to grab a double as above (unless you actually 

> return a double pointer, which will remain valid beyond the extent of 

> the function called). So, you'll need to create a double return value 

> typedef double (* t_double_method)(void *, ...);

> Then get the method pointer with zgetfn or class_getmethod()

> and then call the method appropriately:

> Sorry, if there are typos, as I'm writing this quickly in an airport, 

thanks for the explanation... I tried it and it still crashes... but 

will try also on Mac and with a different compiler on Windows to make 

As long as I call the functions directly everything is working fine. But 

of course, that's not the goal when using obex style objects.

I also noticed that using object_method_typed() returns me an empty 

return value. When I think about it, how does Max know whether my 

function returns A_FLOAT or A_LONG, for example? Do I have to register 

it somewhere indicating the type of return value (smilar to 

class_addmethod() where I tell Max what arguments my function takes in)?

> You can't use a pointer to grab a double as above (unless you  actually 
> return a double pointer, which will remain valid beyond the  extent of 
> the function called). So, you'll need to create a double  return value 
> prototype like the following:
>
> typedef double (* t_double_method)(void *, ...);
>
> Then get the method pointer with zgetfn or class_getmethod()
>
> t_double_method myfn;
>
> myfn = zgetfn(x,gensym("doit"));
>
> and then call the method appropriately:
>
> double retval;
> retval = myfn(x->x_childobj, array);
>
>
> Sorry, if there are typos, as I'm writing this quickly in an airport,  
> but this should give you an idea.

thanks for the explanation... I tried it and it still crashes... but 
will try also on Mac and with a different compiler on Windows to make 
sure it's not another compiler issue.
As long as I call the functions directly everything is working fine. But 
of course, that's not the goal when using obex style objects.

I also noticed that using object_method_typed() returns me an empty 
return value. When I think about it, how does Max know whether my 
function returns A_FLOAT or A_LONG, for example? Do I have to register 
it somewhere indicating the type of return value (smilar to 
class_addmethod() where I tell Max what arguments my function takes in)?

On Jul 1, 2006, at 1:47 AM, Olaf Matthes wrote:

> thanks for the explanation... I tried it and it still crashes... 

> but will try also on Mac and with a different compiler on Windows 

> to make sure it's not another compiler issue.

> As long as I call the functions directly everything is working 

> fine. But of course, that's not the goal when using obex style 

Would be good to see a more complete code example. AFAICT, your 

previous example was crashing because you were dereferencing a double 

*pointer* rather than setting a double *value*, and a double *value* 

Another strategy would be to prototype the method to take a double 

pointer which is set rather than returning the double as the 

function's return value. This can be called with object_method (but 

*not* object_method_typed which is restricted to A_LONG, A_FLOAT, 

A_SYM, A_GIMME, and A_GIMMEBACK typed prototypes). For example.

void myobject_doit(t_myobject *x, double *array, double *rv)

        // do something wih the array

        // then set the "output" argument

// the above should be prototyped A_CANT (untyped) and called as follows

object_method(x->x_childobj, gensym("doit"), array, &rv);

> I also noticed that using object_method_typed() returns me an empty 

> return value. When I think about it, how does Max know whether my 

> function returns A_FLOAT or A_LONG, for example? Do I have to 

> register it somewhere indicating the type of return value (smilar 

> to class_addmethod() where I tell Max what arguments my function 

object_method_typed() requires a typed prototype with the signature 

A_GIMMEBACK for a return value (this is a new introduction for 

methods exposed to JS/Java, and not terribly documented). Otherwise, 

the return value argument is NULL. A_GIMMEBACK is limied to the atom 

type, though an atom can be an object pointer in this case. You could 

in theory create your own object class which wraps a double precision 

Here's a simple example of an A_GIMMEBACK method.

t_max_err obex_tester_gimmeback(t_obex_tester *x, t_symbol *s, long 

    post("obex tester gimmeback av = %d",atom_getlong(av));    

        atom_setlong(rv,atom_getlong(av)*atom_getlong(av));

>
> thanks for the explanation... I tried it and it still crashes...  
> but will try also on Mac and with a different compiler on Windows  
> to make sure it's not another compiler issue.
> As long as I call the functions directly everything is working  
> fine. But of course, that's not the goal when using obex style  
> objects.

Would be good to see a more complete code example. AFAICT, your  
previous example was crashing because you were dereferencing a double  
*pointer* rather than setting a double *value*, and a double *value*  
can't be returned using object_method()

Another strategy would be to prototype the method to take a double  
pointer which is set rather than returning the double as the  
function's return value. This can be called with object_method (but  
*not* object_method_typed which is restricted to A_LONG, A_FLOAT,  
A_SYM, A_GIMME, and A_GIMMEBACK typed prototypes). For example.

void myobject_doit(t_myobject *x,  double *array, double *rv)
{
	if (array&&rv) {
		// do something wih the array
		// then set the "output" argument
		*rv = thevalue;
	}
}

double rv=0;
object_method(x->x_childobj, gensym("doit"), array, &rv);

> I also noticed that using object_method_typed() returns me an empty  
> return value. When I think about it, how does Max know whether my  
> function returns A_FLOAT or A_LONG, for example? Do I have to  
> register it somewhere indicating the type of return value (smilar  
> to class_addmethod() where I tell Max what arguments my function  
> takes in)?

object_method_typed() requires a typed prototype with the signature  
A_GIMMEBACK for a return value (this is a new introduction for  
methods exposed to JS/Java, and not terribly documented). Otherwise,  
the return value argument is NULL. A_GIMMEBACK is limied to the atom  
type, though an atom can be an object pointer in this case. You could  
in theory create your own object class which wraps a double precision  
value, but that seems like more work.

t_max_err obex_tester_gimmeback(t_obex_tester *x, t_symbol *s, long  
ac, t_atom *av, t_atom *rv)
{	
	post("obex tester gimmeback av = %d",atom_getlong(av));	
	if (ac && av) {
		atom_setlong(rv,atom_getlong(av)*atom_getlong(av));
	} else {
		atom_setlong(rv,-1);
	}
	return MAX_ERR_NONE;
}

obex: how to get return values from object_method()