ingo

i want to use a callback-function from an external library, the function which is called does (of course) not pass the t_object *x object to inside of the func.

void callback_search_success(void *ptr) {}

how can i transfer data, to my external-object? lets say to x->ip...

void callback_search_success(void *ptr) {

void *myobj_new(t_symbol *s, short ac, t_atom *av){

    x = (t_obj*)newobject(obj_class);

//// pseudo-code
typedef struct obj
{
	struct object m_ob;
	t_symbol *ip;
} t_obj;

// the callback-function
void callback_search_success(void *ptr) {
    //wanna transfer data from *ptr to *x
}

void *myobj_new(t_symbol *s, short ac, t_atom *av){
	t_obj *x;

using-callback-function

Typically a library will let you specify what the void* is that it passes to your callback. So you tell the library to pass the address of your object and typecast it inside your function.

myobj_new(t_symbol *s, short ac, t_atom *av)

LibrarySetupFunctionThatSpecifiesCallbackParameter(

void*
myobj_new(t_symbol *s, short ac, t_atom *av)
  {
  t_obj *x;

  ///setting up callback-function
  LibrarySetupFunctionThatSpecifiesCallbackParameter(
    /* possibly other stuff... */, x);

// the callback-function
void 
callback_search_success(void *ptr)
  {
  t_obj* myObj = (t_obj*) ptr;
  // do your stuff here
  }


thanks for the reply... but i think i need some help in converting pointers.

normally, the callbackfunction does not need any arguments and is set up like this:

callback.fce_search_success = callback_search_success;

if i just add my object (t_obj x) to the callbackfunction

callback.fce_search_success = callback_search_success(x);

then i get the followig error compiling it:

error C2440: '=': 'void' cannot be converted into 'void (__cdecl *)(void *)'

void (*fce_search_failure)(void *ptr, HWFAULT_T *p_fault);

void (*fce_setup_failure)(void *ptr, HWFAULT_T *p_fault);

void *myobj_new(t_symbol *s, short ac, t_atom *av) {

possible to pass t_myobj to the callback function?

thanks for the reply... but i think i need some help in converting pointers.
normally, the callbackfunction does not need any arguments and is set up like this:
callback.fce_search_success = callback_search_success;

if i just add my object (t_obj x) to the callbackfunction
callback.fce_search_success = callback_search_success(x);

then i get the followig error compiling it:
error C2440: '=': 'void' cannot be converted into 'void (__cdecl *)(void *)'

typedef struct {
  void (*fce_search_success)(void *ptr);
  void (*fce_setup_success)(void *ptr);
  void (*fce_search_failure)(void *ptr, HWFAULT_T *p_fault);
  void (*fce_setup_failure)(void *ptr, HWFAULT_T *p_fault);
} HWUDPS_CALLBACK_T;

void *myobj_new(t_symbol *s, short ac, t_atom *av) {
t_myobj *x;
HWUDPS_CALLBACK_T callback;

//clearing the structure
hwudps_clr_callback_struct(&callback);
//adding callback to search_success
callback.fce_search_success = callback_search_success;
//adding the callback
hwudps_callback(&callback);

possible to pass t_myobj to the callback function?
thanks for any help.

Quote: ingo wrote on Mon, 26 May 2008 14:05

----------------------------------------------------

> if i just add my object (t_obj x) to the callbackfunction

> callback.fce_search_success = callback_search_success(x);

> then i get the followig error compiling it:

> error C2440: '=': 'void' cannot be converted into 'void (__cdecl *)(void *)'

That's not going to work because callbac.fce_search_success is apparently declared as a *pointer to a function*, whereas you are trying to pass it the return value of a function. Two very different animals. Worse still, callback_search_success() is a function that doesn't return anything.

I really can't help you because this is a question about the API to your HWUDPS stuff.

Quote: ingo wrote on Mon, 26 May 2008 14:05
----------------------------------------------------
> if i just add my object (t_obj x) to the callbackfunction
> callback.fce_search_success = callback_search_success(x);
>
> then i get the followig error compiling it:
> error C2440: '=': 'void' cannot be converted into 'void (__cdecl *)(void *)'

I really can't help you because this is a question about the API to your HWUDPS stuff. 

i thought so... i figured out, how to use the objects this api provides, and use cpp now to implement the classes. it works and i can talk to the device...

using callback function