Passing function pointer in place of slot function

Question

While trying to do something like this:

connect(process1, SIGNAL(waitForReadyRead()), this, SLOT(dataReceived_1()));

i have way too many processes for signals. I have created a QList with all those processes (objects).

In order to simplify the code, i wanted to put this connect in a loop and perform this signal slot connection by iterating through the processList.

Something like this:

for(int i=0; i<procList.length(); ++i){
   connect(procList[i], SIGNAL(waitForReadyRead()), this, SLOT(data_rcvd[i]));
}

Here data_rcvd is a QList containing the slot functions.~ but unfortunately we can not add functions inside QList. So i want to know, is there a possibility to define function pointers to achieve this task???

Or you think, i create a new QProcess class (extend) and overload the function waitForReadyRead() to emit a pointer containing this specific information maybe?

How are slots differ for each process? Why don't you connect signals from all processes to a single slot? — vahancho, Jul 23 '19 at 09:03
Do you have a constant set of methods/functions that serve as slots? Is it always 1:1 relation? And how many are we talking about? — tomdol, Jul 23 '19 at 09:07

Vlad from Moscow · Answer 1 · 2019-07-23T08:59:19.683

0

A list may not contain functions but it may contain function pointers. So declare a list of function pointers . In expressions function designators implicitly are converted to pointers to the function types. Pointers are objects.

Here is a demonstrative program that uses the standard container std::list.

#include <iostream>
#include <list>

long long sum( int x, int y ) { return ( long long )x + y; }
long long multiply( int x, int y ) { return ( long long )x * y; }

int main()
{
    std::list<long long( * )( int, int )> lst = { sum, multiply };

    for ( const auto &p : lst ) std::cout << p( 10, 2 ) << '\n';
}

Its output is

12
20

edited Jul 23 '19 at 08:59

answered Jul 23 '19 at 08:51

Vlad from Moscow

301,070
26
186
335

Can you give an example for this? – johny bravo Jul 23 '19 at 08:54
thanks it works fine in general but when i define the function within a class (non static) then it does not compile. I always get this error: reference to non static member function must be called. I can not define function as slots if is declare them globally. Any idea? – johny bravo Jul 23 '19 at 09:58
@johnybravo Use instead template argument of the list like std::function. – Vlad from Moscow Jul 23 '19 at 10:01
Im still learning, could you give some idea? Although not perfect but one workaround as i see, if i declare the member function static it works. Since i will have only one instance of the class doing this, in worse case i will just use this technique then – johny bravo Jul 23 '19 at 10:12
@johnybravo As I already mentioned you can use std;:function. – Vlad from Moscow Jul 23 '19 at 10:17

Passing function pointer in place of slot function

1 Answers1