CODEWITHSUNDEEP
c++omnet++
Wolz
Wolz

Reputation: 23

handleMessage doesnt see my classes and functions

i'm writing this code in omnet++ that should send messages each T time from different nodes to one central node. My problem now is that the handleMessage function doesnt see the classes and function i created, while inizialize sees everything; im fairly new to programming and a newbie to the c++ language :). CODE:

using namespace omnetpp;
class Net : public cSimpleModule
{
public:   
    virtual void initialize() override;
    virtual void handleMessage(cMessage *msg) override;
};

class Central_Node : public Net
{
    simtime_t time_stamps[];
    int index;

public:
    void addTimeStamp()
    {
      int array_size = sizeof(time_stamps);
      time_stamps[array_size] = SimTime();
    }
    void deleteSignal(cMessage *msg)
    {
        delete msg;
    }
};

class Sensor : public Net
{
    int index;
    double delay;

public:
    Sensor(int a, double b)
    {
        index = a;
        delay = b;
    }

    void sendMessage()
    {
        cMessage *msg = new cMessage("Signal");
        send(msg, 0);
        cMessage *SelfMsg = new cMessage("SelfMessage");
        scheduleAt(simTime() + delay, SelfMsg);
    }
};


Define_Module(Net);

void Net::initialize()
{    
    Central_Node centralNode;
    Sensor Sensor1 (1,100);
    Sensor Sensor2 (2,210);

    Sensor1.sendMessage();
    Sensor2.sendMessage();
}

void Net::handleMessage(cMessage *msg)
{
    if (getIndex() == 0) 
    {
        simtime_t ArrivalTime = centralNode.addTimeStamp();
        centralNode.deleteSignal(*msg);
    }

    if (getIndex() == 1) 
    {
        Sensor1.sendMessage();
    }

    if (getIndex() == 2) 
    {
       Sensor2.sendMessage();
    }
}

The error I get is: use of undeclared identifier 'centralNode' on the line simtime_t ArrivalTime = centralNode.addTimeStamp();.

Upvotes: 2

Views: 169

Answers (1)

NicholasM
NicholasM

Reputation: 4673

The problem is that at the point of use, centralNode is not a defined variable:

void Net::handleMessage(cMessage *msg)
{
  if (getIndex() == 0) 
  {
      // Error:  use of undeclared identifier 'centralNode'
      simtime_t ArrivalTime = centralNode.addTimeStamp();  
      centralNode.deleteSignal(*msg);
  }
  [...]
}

You create a centralNode variable in the Net::initialize() member function, but that is a local variable within the function, not a class member. That centralNode variable in the Net::initialize() function is naturally not visible within any other member functions, including the Net::handleMessage member function.

There are two possible solutions.

Option 1: Create a local variable in Net::handleMessage

You can declare a local variable in Net::handleMessage(), just like the Net::initialize() function does. This Central_Node object will "disappear" (be destroyed) once it goes out of scope.

void Net::handleMessage(cMessage *msg)
{
  if (getIndex() == 0) 
  {
      Central_Node centralNode;    // Instantiate here before use.
      simtime_t ArrivalTime = centralNode.addTimeStamp();  
      centralNode.deleteSignal(*msg);
  }
  [...]
}

Option 2: Create a data member in the Net class

You can declare a class data member in the Net class. This is complicated, however, because the Net class would contain a Central_Node data member, but the CentralNode class itself inherits from Net.

To break this circular dependency, you can forward-declare Central_Node and use a pointer within the Net class:

class Central_Node;  // Forward declaration

class Net : public cSimpleModule
{
    // unique_ptr required to break circular dependency
    std::unique_ptr<Central_Node> centralNode;
    [...]
};

General Comments

Often, when code exhibits a circular dependency, it is a sign that the abstractions or relationships expressed in code are not the right ones.

In this case, it seems wrong that a Central_Node inherits from a Net (presumably "Network") class. Inheritance is classically used to express an "is-a" relationship, and it is very odd to say "A Central_Node (or any Node) is a Network". Instead, a Node (including a CentralNode) is a part of a Network, or alternatively, a Network contains Nodes.

Separately from all this, I think there is a bug in the Central_Node:: addTimeStamp() member function, since the array data member is never initialized. I suspect that, as written, this will cause a segfault or other crash at runtime.

Upvotes: 1

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