generalize a c++ method

jsulm

i think i can not use this last solution

Sure you can: you pass the pointer to second method when you call the first method, right? And since both methods are not static you call the first method already on an instance (which is "this" inside the method):

this->*method(); // method is the pointer to the other method

ODБOï

@jsulm said in generalize a c++ method:

: you pass the pointer to second method when you call the first method, right?

Yes, but it only works if the
2nd method is static !

//first 
void uaSub(QScopedPointer<QOpcUaNode> &node, QString nodeId , void (*theUpdateHandler)(QOpcUa::NodeAttribute attr,const QVariant &value)){...}
// 2nd
static void nIndexUpdated(QOpcUa::NodeAttribute attr, const QVariant &value){...}


uaSub(nIndexNode,"ns=4;s=MAIN.nIndex",*nIndexUpdated){...}

//Here **nIndexUpdated** must be static !  no ?

if it is not static i get :
reference to non-static member function must be called error

jsulm

@LeLev Please take a closer look at the snippet I provided before:

typedef void (T::*MethodPtr) ();
MethodPtr method = &T::MethodA;
T *obj = new T();
obj->*method();

Your syntax is not even correct as you have to use & to get a pointer not *
So in your case something like

class A
{
    typedef void (A::*MethodPtr) ();
    void nIndexUpdated() {}
    void uaSub(..., MethodPtr ptr) {
        this->*ptr();
    }

    // Somewhere inside class A you call uaSub
    uaSub(/*params*/, &A::nIndexUpdated);
}

ODБOï

@jsulm
thank you so much for the help you provide.
Unfortunately i'm so bad, i can't make this work

class MachineBackend : public QObject
{
    typedef void (MachineBackend::*MethodPtr) ();
    Q_OBJECT

void nIndexUpdated(QOpcUa::NodeAttribute attr, const QVariant &value){...}

void uaSub2(QScopedPointer<QOpcUaNode>&node, QString nodeId, MethodPtr updateHandlerPtr){
       
       this->*updateHandlerPtr(); // < error here 

    }
};

called object type 'MachineBackend ::MethodPtr' (aka 'void (MachineBackend ::*)()' ) is not a function or function pointer

jsulm

@LeLev Try

this->updateHandlerPtr();

ODБOï

@jsulm said in generalize a c++ method:

this->updateHandlerPtr();

yes i did also, in that case error is :

no member named 'updateHandlerPtr' in 'MachineBackend '
which is true

jsulm

@LeLev This should compile:

(this->*updateHandlerPtr)();

Method pointers are a mess :-)

ODБOï

yes now it doas. awesome ! thank you so much!

class MachineBackend : public QObject
{
    typedef void (MachineBackend::*MethodPtr) ();
    Q_OBJECT

void nIndexUpdated(QOpcUa::NodeAttribute attr, const QVariant &value){...}

void uaSub2(QScopedPointer<QOpcUaNode>&node, QString nodeId, MethodPtr updateHandlerPtr){
       
       (this->*updateHandlerPtr)();

    }
};

there is still an issue in the usSub() call

//  Somewhere inside class
  uaSub2(nIndexNode,"ns=4;s=MAIN.nIndex", MachineBackend::nIndexUpdated);  // << error
//

error : reference to non-static member function must be called

im trying every possible syntax right now ...

jsulm

@LeLev said in generalize a c++ method:

uaSub2(nIndexNode,"ns=4;s=MAIN.nIndex", MachineBackend::nIndexUpdated);

uaSub2(nIndexNode,"ns=4;s=MAIN.nIndex", &MachineBackend::nIndexUpdated);

jsulm

@LeLev This small example works for me:

#include <iostream>

class A
{
public:
    typedef void (A::*MethodPtr) ();
    void someMethod() { std::cout << "Hallo!" << std::endl; }
    void uaSub2(MethodPtr updateHandlerPtr){
       (this->* updateHandlerPtr)();
    }
};

int main()
{
    A a;
    a.uaSub2(&A::someMethod); 
    return 0;
}

ODБOï

@jsulm yes sorry that is the first one i have tryed:

uaSub2(nIndexNode,"ns=4;s=MAIN.nIndex", &MachineBackend::nIndexUpdated);

// err :  cannot initialize a parameter of type 'Machinebackend::MethorPtr' (aka 'void (MAchinebackend::*)()') with an rvalue of type 'void (MAchineBAckend::*)(QOpcUa::NodeAttribute, const QVariant &)' : different number of parameters (0 vs 2)

error : no matching function for call to 'MachineBackend::uaSub2(QScopedPointer<QOpcUaNode>&, const char [19], <unresolved overloaded function type>)'
         uaSub2(nIndexNode,"ns=4;s=MAIN.nIndex",MachineBackend::nIndexUpdated);
                                                                             ^

jsulm

This post is deleted!

jsulm

@LeLev said in generalize a c++ method:

nIndexUpdated

This one has parameters, you need to adapt your typedef for the pointer accordingly.
This is what the error tells you.

ODБOï

@jsulm

class MachineBackend : public QObject
{
    typedef void (MachineBackend::*MethodPtr) ();
    Q_OBJECT

void nIndexUpdated(QOpcUa::NodeAttribute attr, const QVariant &value){...}

void uaSub2(QScopedPointer<QOpcUaNode>&node, QString nodeId, MethodPtr updateHandlerPtr){
       
       (this->*updateHandlerPtr)();

    }
};

in the constructor of this class i call m_client.connectToServer(), then connect stateChanged signal of the m_client to a method where i want to create the subscriptions :

 QObject::connect(m_client.data(), &QOpcUaClient::stateChanged, this, &MachineBackend::clientStateHandler);

void MachineBackend::clientStateHandler(QOpcUaClient::ClientState state)
{
    setConnected((state == QOpcUaClient::ClientState::Connected)); 

    if (state == QOpcUaClient::ClientState::Connected) {// if client is connected i create subscriptions
                 
        // uaSub(nIndexNode,"ns=4;s=MAIN.nIndex",*nIndexUpdated); // function pointer to static function

        // uaSub1(nIndexNode,"ns=4;s=MAIN.nIndex", MachineBackend::NINDEX) // enum
        
         uaSub2(nIndexNode,"ns=4;s=MAIN.nIndex",&MachineBackend::nIndexUpdated);   

    }

   [...]
}

I think i have to adapt my typedef because &QOpcUaClient::stateChanged returns 2 parameters

jsulm

@LeLev said in generalize a c++ method:

I think i have to adapt my typedef

Yes, you have to specify the parameter types when defining a function/method pointer type.

ODБOï

i'm having troubles to adapt the typedef..
should it be

typedef void (MachineBackend::*MethodPtr) (QOpcUa::NodeAttribute attr,const QVariant &value);

 or 

typedef void (MachineBackend::*MethodPtr(QOpcUa::NodeAttribute attr,const QVariant &value)) ();

jsulm

@LeLev said in generalize a c++ method:

typedef void (MachineBackend::*MethodPtr) (QOpcUa::NodeAttribute attr,const QVariant &value);

typedef void (MachineBackend::*MethodPtr) (QOpcUa::NodeAttribute, const QVariant&);

No need for parameter names, only types.

ODБOï

@jsulm

class MachineBackend : public QObject
{
    typedef void (MachineBackend::*MethodPtr) (QOpcUa::NodeAttribute, const QVariant&);

    Q_OBJECT

public:
    void uaSub2(QScopedPointer<QOpcUaNode>&node, QString nodeId, MethodPtr updateHandlerPtr){
 
      //  trying to use lambda to call my pointed function but can't

      /*  QObject::connect(node.data(),&QOpcUaNode::attributeUpdated,[&]{
             (this->*updateHandlerPtr() ) ();
        });
     */ 
  
         // maybe  is it possible to connect to my function directly  ?     
     QObject::connect(node.data(),&QOpcUaNode::attributeUpdated,this,&MachineBackend:: ??)

    }
    

};

jsulm

@LeLev said in generalize a c++ method:

(this->*updateHandlerPtr() ) ();

(this->*updateHandlerPtr) (); <--- You have to pass 2 parameters to it!

ODБOï

@jsulm yes but i don't have any parameter to pass to it .. .

its just a handler function that must be connected to
QOpcUaNode::attributeUpdated witch returns 2 values ;

that is why it has to have 2 params.

I don't want to call that function, i want it to be connected to

QOpcUaNode::attributeUpdated , and called automatically when attributeUpdated is emitted in the opcua backend