How to Dynamically Declare an Array of Objects with a Constructor in C++ - A Step-by-Step Guide

Written by: Manish Methani

November 14, 2023 at 2:04pm IST. 6 min 19 sec

Introduction

In C++, you can create arrays of objects that are initialized with a constructor. This allows you to allocate and manage a dynamic array of objects with specific properties. In this step-by-step guide, we will walk you through the process of dynamically declaring an array of objects with a constructor in C++, complete with an example code to illustrate the concept.

Table of Contents:

Step 1: Include Necessary Headers

Start by including the necessary headers for C++ programming:

#include <iostream>
#include <vector>

Step 2: Define the Class

• We define a class named MyObject. This class represents the type of object that we want to store in the dynamic array. The class has the following components:
  • A public constructor: It takes two parameters, id and name, and initializes the object's properties.
  • A public member function display(): This function is marked as const to indicate that it does not modify the object. It is responsible for displaying the object's properties using std::cout.

class MyObject {
public:
    MyObject(int id, std::string name) : id(id), name(name) {}

    void display() const {
        std::cout << "ID: " << id << ", Name: " << name << std::endl;
    }

private:
    int id;
    std::string name;
};

Step 3: Declare Variables and Create a Vector

• In the main() function, we declare a variable arraySize and set it to 5, indicating the desired size of the dynamic array.
• We create a std::vector named objectArray to store instances of the MyObject class. This is a dynamic array that can grow or shrink as needed.

int main() {
    int arraySize = 5;
    std::vector objectArray;

Step 4: Populate the Dynamic Array

• We use a for loop to populate the dynamic array. For each iteration, we create a new MyObject instance with a unique id and a name constructed as "ObjectX," where X is the loop iteration.
• The push_back function is used to add the newly created MyObject to the objectArray.

    for (int i = 1; i <= arraySize; i++) {
        objectArray.push_back(MyObject(i, "Object" + std::to_string(i)));
    }

Step 5: Access and Display Array Elements

• We use a range-based for loop to iterate through the objectArray.
• The const qualifier ensures that the display function is called on a constant object, preventing any modification of the objects within the loop.
• Inside the loop, we call the display function for each MyObject instance, which prints the object's properties.

for (const MyObject& obj : objectArray) {
        obj.display();
    }

Step 6: Complete the Main Function

return 0;
}

In summary, this code demonstrates how to dynamically declare and initialize an array of objects using a std::vector. The MyObject class represents the objects to be stored in the array, and the code shows how to create, populate, and display the objects within the dynamic array.

Full Example Code

#include <iostream>
#include <vector>

class MyObject {
public:
    MyObject(int id, std::string name) : id(id), name(name) {}

    void display() const {
        std::cout << "ID: " << id << ", Name: " << name << std::endl;
    }

private:
    int id;
    std::string name;
};

int main() {
    int arraySize = 5;
    std::vector objectArray;

    for (int i = 1; i <= arraySize; i++) {
        objectArray.push_back(MyObject(i, "Object" + std::to_string(i)));
    }

    for (const MyObject& obj : objectArray) {
        obj.display();
    }

    return 0;
}

Output:

ID: 1, Name: Object1
ID: 2, Name: Object2
ID: 3, Name: Object3
ID: 4, Name: Object4
ID: 5, Name: Object5