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  • In this article, you'll learn to manage memory effectively in C++ using new and delete operations.
 cpp memory management
  • Arrays can be used to store multiple homogenous data but there are serious drawbacks of using arrays.
  • You should allocate the memory of an array when you declare it but most of the time, the exact memory needed cannot be determined until runtime.
  • The best thing to do in this situation is to declare an array with maximum possible memory required (declare array with maximum possible size expected).
  • The downside to this is unused memory is wasted and cannot be used by any other programs.
  • To avoid wastage of memory, you can dynamically allocate memory required during runtime using new and delete operator in C++.
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Example 1: C++ Memory Management

  • C++ Program to store GPA of n number of students and display it where n is the number of students entered by user.
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    learn c++ tutorials - memory management in c++ Example

#include <iostream>
#include <cstring>
using namespace std;

int main()
{
    int num;
    cout << "Enter total number of students: ";
    cin >> num;
    float* ptr;
    
    // memory allocation of num number of floats
    ptr = new float[num];

    cout << "Enter GPA of students." << endl;
    for (int i = 0; i < num; ++i)
    {
        cout << "Student" << i + 1 << ": ";
        cin >> *(ptr + i);
    }

    cout << "\nDisplaying GPA of students." << endl;
    for (int i = 0; i < num; ++i) {
        cout << "Student" << i + 1 << " :" << *(ptr + i) << endl;
    }

    // ptr memory is released
    delete [] ptr;

    return 0;
}

Output

Enter total number of students: 4 
Enter GPA of students.
Student1: 3.6
Student2: 3.1
Student3: 3.9 
Student4: 2.9

Displaying GPA of students.
Student1 :3.6
Student2 :3.1
Student3 :3.9
Student4 :2.9
  • In this program, only the memory required to store num (entered by user) number of floating-point data is declared dynamically.

The new Operator

ptr = new float[num];
  • This expression in the above program returns a pointer to a section of memory just large enough to hold the num number of floating-point data.
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The delete Operator

  • Once the memory is allocated using new operator, it should released back to the operating system.
  • If the program uses a large amount of memory using new, system may crash because there will be no memory available for the operating system.
  • The following expression returns memory back to the operating system.
  • The brackets [] indicates the array has been deleted. If you need to delete a single object then, you don't need to use brackets.
delete ptr;

Example 2: C++ Memory Management

Object-oriented approach to handle above program in C++.
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#include <iostream>
using namespace std;

class Test
{                                                                                                                                                                                                                                                                                    
private:
    int num;
    float *ptr;

public:
    Test()
    {
        cout << "Enter total number of students: ";
        cin >> num;
        
        ptr = new float[num];
        
        cout << "Enter GPA of students." << endl;
        for (int i = 0; i < num; ++i)
        {
            cout << "Student" << i + 1 << ": ";
            cin >> *(ptr + i);
        }
    }
    
    ~Test() {
        delete[] ptr;
    }

    void Display() {
        cout << "\nDisplaying GPA of students." << endl;
        for (int i = 0; i < num; ++i) {
            cout << "Student" << i+1 << " :" << *(ptr + i) << endl;
        }
    }
    
};
int main() {
    Test s;
    s.Display();
    return 0;
}
  • The output of this program is same as the above program.
  • When the object is created, the constructor is called which allocates the memory for num floating-point data.
  • When the object is destroyed, i.e, when the object goes out of scope, destructor is automatically called.
    ~Test() {
        delete[] ptr;
    }
  • This destructor executes delete[] ptr; and returns memory back to the operating system.

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