how can i know how many slots connected to a signal?

[yj_yulin]

if i can know this, i can reduce some object produce and even can drop the emit action.
thanks in advance.

[aamer4yu]

Wont it be better if you dont connect the slot to the signal.
Not emitting the signal cud hamper your functionality,, after all why is a signal used ?
hope am right

[wysota]

Emiting a signal is very cheap. It's a simple function call. If there are no slots connected, nothing more will happen.

[jpn]

See QObject::receivers().

[ktk]

Emiting a signal is very cheap. It's a simple function call. If there are no slots connected, nothing more will happen.

Well, it goes through MetaObject::activate() in any case. It will indeed return fairly early if nothing is connected, but it certainly is a bit more expensive than a single function call.

[yj_yulin]

Emiting a signal is very cheap. It's a simple function call. If there are no slots connected, nothing more will happen.

signals:
void a_happend(Tsomeobject * obj, int x, int y);

yeah, though signal is cheap, the object need to create(Tsomeobject * obj) maybe not.

and my situation also relate to the object management,thus if i can know there is no slots connected to the signal, it can reduce more work.

thanks for all involved, and especially to jpn.

[wysota]

Well, it goes through MetaObject::activate() in any case. It will indeed return fairly early if nothing is connected, but it certainly is a bit more expensive than a single function call.

I didn't say "single" :) Emiting a signal takes about 5-6 function calls but these are cheap compared to actual actions you take in the slot itself.


yeah, though signal is cheap, the object need to create(Tsomeobject * obj) maybe not.
Yes, that's true. If you create an expensive object only to emit a signal then that's certainly a good idea to avoid the emission.