[QT4] threads, signals, and slots, please help.

[wysota]

Since I wanted it to, naturally.

Actually, I was mislead by statements (elsewhere) that emit was "just a decoration for the programmer", that the signal was still "just a function call".

It is (usually) a function call. But! What happens if there are two or more slots connected to a signal? Return value of which of them should then be returned?

As soon as I figure out just what you mean, I'm sure I'll try it.

I mean to pass a pointer or reference of the object which is to deliver some information to the other one. This way you'll be able to call the method directly on a single object, without signal/slot mechanism:

struct aaa {
    int action(someclass &);
}; 
 
class bbb {
public:
    void registerDeliverer(aaa *a){ m_ad = a; }
    void do_something();
private:
aaa *m_ad;
}
 
void bbb::do_something(){
//...
  if(!m_ad) 
    return;
  int act = m_ad->action(); // fetch an int from registered object
//...
}
//...
aaa action_deliverer;
bbb obj;
//...
obj->registerDeliverer(&action_deliverer);
//...
obj->do_something();
//...

struct aaa {
    int action(someclass &);
}; 

class bbb {
public:
    void registerDeliverer(aaa *a){ m_ad = a; }
    void do_something();
private:
aaa *m_ad;
}

void bbb::do_something(){
//...
  if(!m_ad) 
    return;
  int act = m_ad->action(); // fetch an int from registered object
//...
}
//...
aaa action_deliverer;
bbb obj;
//...
obj->registerDeliverer(&action_deliverer);
//...
obj->do_something();
//...

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[ucntcme]

It is (usually) a function call. But! What happens if there are two or more slots connected to a signal? Return value of which of them should then be returned?

Well obviously the only one I am interested in!

Seriously though, that makes sense explained that way.
Perhaps it would be nice if a warning/error was issued at compile time if a signal was declared as anything other than void? As a newbie that would make some sense to me, and would have alerted me to the head-banging route I was travelling upon.

I mean to pass a pointer or reference of the object which is to deliver some information to the other one. This way you'll be able to call the method directly on a single object, without signal/slot mechanism:

struct aaa {
    int action(someclass &);
}; 
 
class bbb {
public:
    void registerDeliverer(aaa *a){ m_ad = a; }
    void do_something();
private:
aaa *m_ad;
}
 
void bbb::do_something(){
//...
  if(!m_ad) 
    return;
  int act = m_ad->action(); // fetch an int from registered object
//...
}
//...
aaa action_deliverer;
bbb obj;
//...
obj->registerDeliverer(&action_deliverer);
//...
obj->do_something();
//...

struct aaa {
    int action(someclass &);
}; 

class bbb {
public:
    void registerDeliverer(aaa *a){ m_ad = a; }
    void do_something();
private:
aaa *m_ad;
}

void bbb::do_something(){
//...
  if(!m_ad) 
    return;
  int act = m_ad->action(); // fetch an int from registered object
//...
}
//...
aaa action_deliverer;
bbb obj;
//...
obj->registerDeliverer(&action_deliverer);
//...
obj->do_something();
//...

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I suspected that was what you meant, and had begun working on that. Of course, I've done it wrong and get segfaults, but I'm sure it's not a Qt related segfault, rather programmer naivete. Some of it I just *have* to bang away at until I get it. But then again, once I get it, I've got it. Know what I mean?


But one quick question on the above ... what is "someclass" representing?

[wysota]

Perhaps it would be nice if a warning/error was issued at compile time if a signal was declared as anything other than void? As a newbie that would make some sense to me, and would have alerted me to the head-banging route I was travelling upon.

No, because slots are regular methods, just with additional capabilities. You can invoke them as normal methods and use their return values as usual.

But one quick question on the above ... what is "someclass" representing?

Some data which is processed by "action" method... That's just an example, nothing specific.

[ucntcme]

No, because slots are regular methods, just with additional capabilities. You can invoke them as normal methods and use their return values as usual.

Well it was a nice thought anyway.

Some data which is processed by "action" method... That's just an example, nothing specific.

Well I finally found the route out of segfault land (a nap can do wonders ) and it is all working perfectly. Thanks again!