array class member, with dynamically changeable length during runtime - c++

Question

I am trying to make a network application. Its class blueprint is roughly like this-
class Node
{
public:
// member functions
private:
int nodeID;
// other members
};
class NodeNetwork
{
public:
// member functions
private:
Node nodeArray[MAX_NODES];
// other members
};
Here, the Node class will deal with each node and the NodeNetwork is used to deal with the complete network.
The actual number of nodes in nodeArray can vary from 0 to MAX_NODES during runtime, i.e., it may not always be MAX_NODES, the number of nodes can be increased or decreased during runtime. Moreover, when the program starts the number will always be 0, after that it will start increasing.
I am using Node nodeArray[MAX_NODES];, but I think it's a serious wastage of space as not always I will have MAX_NODES nodes at runtime. So I am looking for ways to optimize it. I want it so that it starts with a zero-length array, but the size can be increased or decreased subjected to the above constraints based on the nodes added or removed at runtime. I researched on the internet but did not find any concrete answer.
I hope someone can help me solve this problem, thanks in advance.

Answer 1

You can use dynamically array allocation for this purpose:
int* arr = new int[5];
..and anytime you wish to change the number of elements:
int size = 5;
int* arr = new int[size] {};
int* new_arr = new int[size + 1];
for (int i = 0; i < size; i++)
{
new_arr[i] = arr[i];
}
delete[] arr;
arr = new_arr;
// Now arr has a storage capacity of 6 elements
..so for your case you can write:
Node* nodeArray = nullptr; // nullptr == null pointer
But this can take a lot of time for huge arrays.
So preferably, you can use std::vector:
#include <iostream>
#include <vector>
int main()
{
std::vector<int> vec{ 1, 2, 3, 4, 5 };
vec.push_back(6); //Insert a new element
std::cout << vec[0]; // Accessing an element is the same as an array
}
..so for your case:
// {} is just for initialization, not exactly mandatory
std::vector<Node> nodeArray{};

Answer 2

You can use std::vector instead of array. That is, you can make the data member nodeArray to be a std::vector<Node> as shown below.
#include <iostream>
#include<vector>
class Node
{
public:
//constructor for initializing nodeID data member
Node(int pnodeID): nodeID(pnodeID)
{
}
//getter for nodeId
int getId() const
{
return nodeID;
}
private:
//always initialize built in type in local/block scope so that they don't have indeterminate value
int nodeID = 0;
// other members
};
class NodeNetwork
{
public:
// member function to add Node
void addNode(const Node& n)
{
nodeArray.push_back(n);
}
//member function to print out the current nodes
void display() const
{
std::cout<<"Network has the following nodes: "<<std::endl;
for(const Node& elem: nodeArray)
{
std::cout<<elem.getId()<<std::endl;
}
}
private:
std::vector<Node> nodeArray; //used std::vector instead of array
// other members
};
int main()
{
//create Node objects
Node node1{1};
Node node2{2};
Node node3{3};
NodeNetwork network1;
//add node1 into the network1's nodeArray data member
network1.addNode(node1);
//add node2 into the network1's nodeArray data member
network1.addNode(node2);
//display all nodes into network1
network1.display();
return 0;
}
In the above demo we have added elements into the nodeArray data member by using std::vector::push_back member function.
The output of the above program can be seen here:
Network has the following nodes:
1
2