Dynamic Memory Allocation in CPP: An Easy Guide.

Introduction

Dynamic Memory Allocation in C++ involves the on-the-fly management of memory during program execution. This is achieved using the “new” operator to allocate memory and the “delete” operator to free up memory previously allocated using “new”. By utilizing these operators, programs can dynamically allocate memory as needed, ensuring efficient memory utilization while the program is running.

In this article, we’ll explore this powerful concept and understand why it’s essential. We’ll learn how to allocate memory on the go, create flexible data structures, and manage memory efficiently. So, get ready to unleash the full potential of your programs with dynamic memory allocation! Let’s begin!

C++ Program Memory Management

When we execute a C++ program on our computer, it needs a place to keep its instructions, variables, and functions. This space is called “memory.” It’s like a storage area where the program stores all the things it needs while running.

There are two types of memory in our computer system: Static Memory and Dynamic Memory.

Static Memory: This is a fixed amount of memory allocated by the operating system when a C++ program is compiled. It uses a data structure called a stack to manage this memory. The space taken by the program remains constant until it finishes running.

Dynamic Memory: This memory can be allocated or freed by the operating system while a C++ program is running. It’s more flexible than static memory because we can give back memory we no longer need and use it again later in the program. This makes our program more efficient in managing memory resources during runtime.

A C++ program’s memory usage can be divided into four main parts:

• Run-time Stack (Static Memory): This is where the program keeps track of function calls and local variables. It’s like a temporary storage area for function execution.
• Static Data Memory (Global and Static Variables): Here, memory is allocated for variables that are declared globally or with the “static” keyword. These variables retain their values throughout the program’s execution.
• Instructions / Statements (Static Memory): This section holds the actual code instructions or statements of the program. It’s where the program’s logic and operations are stored.
• Heap (Dynamic Memory): This is the area for dynamic memory allocation during runtime. It’s used when you need to allocate memory at runtime, like when creating objects or arrays.

The Stack memory

• Stack memory is a fixed space set aside by the operating system during program compilation.
• It stores functions, variables, and local statements within function definitions.
• Stack is a subset of static memory, a part of the computer’s memory storage.
• It’s used to manage the flow of execution, like function calls and returns.
• Stack memory allocation is done at compile-time, ensuring a predetermined space for program components.
• Variables created in a function are allocated in stack memory.
• Stack memory is efficient for managing local data due to its predictable and organized structure.

The Heap Memory

• Heap memory is dynamic memory in the system.
• It’s a sizable memory block that can grow or shrink while the program runs.
• Memory allocation and deallocation are done using new and delete operators in C++.
• The heap can expand as long as machine memory is available.
• Careful usage is essential to prevent memory exhaustion and errors.

Types of Memory Allocation

• Static Memory Allocation: Memory is allocated at compile time and remains fixed during program execution.
• Dynamic Memory Allocation: Memory is allocated during runtime using functions like ‘malloc()‘ and ‘new‘.
• Automatic Memory Allocation: Variables are allocated and deallocated automatically in the stack.
• Manual Memory Allocation: The programmer is responsible for allocating and deallocating memory in the heap.
• Global Memory Allocation: Memory is allocated globally and can be accessed from anywhere in the program.
• Local Memory Allocation: Memory is allocated locally within a function’s scope.
• Contiguous Memory Allocation: Allocates a block of memory in a continuous sequence.
• Non-Contiguous Memory Allocation: Allocates memory in non-sequential chunks, used in dynamic data structures.
• Buddy Memory Allocation: Memory is divided into blocks of fixed size, split as needed for allocation.
• Memory Pool Allocation: Pre-allocated memory pool is used for allocating fixed-size memory chunks.
• Best Fit Memory Allocation: Allocates the smallest free block that fits the requested size.
• Worst Fit Memory Allocation: Allocates the largest free block, leaving smaller fragments.
• First Fit Memory Allocation: Allocates the first free block that fits the requested size.
• Next Fit Memory Allocation: Allocates the next free block after the last allocation.

Why Dynamic Memory Allocation?

Dynamic memory allocation is a way to create objects in your program when you’re not sure how many you’ll need beforehand. Imagine you’re making a program where users can input data, like a list of students’ names. If you knew in advance how many students there would be, you could create an array of names to store the data. But what if the number of students could change each time the program runs? That’s where dynamic memory allocation comes in.

With dynamic memory allocation, you can ask the computer to create a memory for your data while the program is running. This way, you don’t need to decide how much memory you need beforehand. It’s like telling the computer, “Hey, I need some space to store this data, and I’ll tell you how much later.”

This is really useful because it lets your program be more flexible. You can create as much memory as you need, and when you’re done using it, you can give it back to the computer. It’s like borrowing a book from the library – you get it when you need it and return it when you’re done.

So, dynamic memory allocation helps you make programs that can adapt to different situations and use memory efficiently. It’s like having a magic tool that creates space for your data whenever you need it.

How is it Different from Memory Allocated to Normal Variables?

1. Static Memory Allocation:
   The operating system allocates memory for regular variables and arrays like int r;, double arr[10];, char name[20];. This memory is set at compile-time and automatically released when the function, block, or program finishes. The operating system manages this process.
2. Dynamic Memory Allocation:
   The operating system handles dynamic memory allocation for variables created using the new keyword, like int* ptr = new int;, int* arr = new int[6];. This memory is allocated during runtime and persists until the program ends. It’s the programmer’s responsibility to deallocate this memory when it’s no longer needed. If not done, memory leaks can occur, leading to inefficient use of memory resources.

How is Memory Allocated/De-Allocated in C++?

In C Language, when we need to allocate or deallocate memory dynamically during program execution, we include the header file. This allows us to use functions like malloc(), calloc(), realloc(), and free().

In C++ Language, the new and delete operators are already present in the C++ Standard Library. This means we don’t need to include any specific library file for managing memory allocation and deallocation during runtime. However, C++ also supports functions like malloc() and calloc() from C by including the header file, thanks to its compatibility with C Language. This article focuses on explaining the usage of C++’s new and delete operators for memory management.

Comparison with “malloc()”, “calloc()”, and “free()” Functions of C.

Dynamic Memory Allocation & De-allocation Criteria

Dynamic Memory Allocation in C++:

• Allocate Space: To allocate memory dynamically, we use the “new” operator to create space in the heap memory.
• Use Pointer: We store the address of the allocated space in a pointer variable to work with the memory contents.
• Free Memory: When the memory is no longer needed, we use the “delete” operator to release the allocated space and free up heap memory.

Dynamic Memory Allocation in C++ for Arrays

Dynamic memory allocation in C++ is a technique that allows you to allocate memory for variables or data structures like arrays at runtime. Unlike static memory allocation, where memory is allocated during compile-time and remains fixed, dynamic memory allocation gives you flexibility by allowing memory to be allocated or deallocated while the program is running.

When you allocate memory dynamically for an array, you can specify the size of the array based on user input or other runtime factors. This can be very useful when you don’t know the exact size of the array beforehand or if the size might change during the program’s execution.

To dynamically allocate memory for an array in C++, you use the new keyword, and to deallocate it, you use the delete keyword. Here’s a simple breakdown:

Allocating Memory:

   int size;
   cout << "Enter the size of the array: ";
   cin >> size;

   int *dynamicArray = new int[size];

In this example, dynamicArray is a pointer to an integer. It is used to hold the memory address of the first element of the dynamically allocated array. The new keyword allocates memory for size integers.

Accessing and Using the Dynamically Allocated Array:

   for (int i = 0; i < size; i++) {
       dynamicArray[i] = i * 10;
   }

This loop fills the dynamically allocated array with values.

Deallocating Memory:

   delete[] dynamicArray;

This line of code deallocates the memory that was allocated for the dynamic array. It’s important to use delete[] instead of just delete to indicate that you are deallocating an array.

Using dynamic memory allocation for arrays can be very useful when you need to work with arrays whose sizes are determined during program execution. However, it’s important to remember to deallocate the memory using delete[] to avoid memory leaks.

Example:

#include 
using namespace std;

int main() {
    int size;
    cout << "Enter the size of the array: ";
    cin >> size;

    int *dynamicArray = new int[size];

    for (int i = 0; i < size; i++) {
        dynamicArray[i] = i * 10;
    }

    cout << "Array elements: ";
    for (int i = 0; i < size; i++) {
        cout << dynamicArray[i] << " ";
    }
    cout << endl;

    delete[] dynamicArray;

    return 0;
}

Output:

Enter the size of the array: 5
Array elements: 0 10 20 30 40

Explanation:

• User Input: The program asks the user to input the desired size of the array.
• Dynamic Allocation: Memory is dynamically allocated for the array based on the user’s input using the new keyword.
• Array Filling: A loop fills the allocated array with values calculated using a formula.
• Printing Array: The program prints the elements of the dynamically allocated array.
• Memory Deallocation: To prevent memory leaks, the memory allocated for the array is released using the delete[] keyword.

Dynamic Memory Allocation in C++ for Objects

Dynamic memory allocation in C++ is a technique that allows you to create objects at runtime, instead of at the time of program compilation. This is especially useful when you don’t know the exact number of objects you need in advance or when you want to manage memory more efficiently.

When you allocate memory dynamically for objects, you use the new operator followed by the class name and parentheses. This allocates memory from the heap, a region of memory used for dynamic memory allocation. Here’s the syntax:

Classname *pointer_name = new Classname;

Let’s say you have a simple class called Student:

class Student {
public:
    string name;
    int age;
};

You can allocate memory for a Student object like this:

Student *studentPtr = new Student;

This allocates memory for a Student object and returns a pointer to that memory location, which is stored in the studentPtr.

After you’re done using the dynamically allocated object, you should release the memory to avoid memory leaks using the delete operator:

delete studentPtr;

Now, let’s see a practical example. Suppose you want to dynamically create an array of Student objects:

#include 
using namespace std;

class Student {
public:
    string name;
    int age;
};

int main() {
    int numStudents;
    cout << "Enter the number of students: ";
    cin >> numStudents;

    Student *students = new Student[numStudents];

    for (int i = 0; i < numStudents; i++) {
        cout << "Enter name and age for student " << i + 1 << ": ";
        cin >> students[i].name >> students[i].age;
    }

    for (int i = 0; i < numStudents; i++) {
        cout << "Student " << i + 1 << ": Name - " << students[i].name << ", Age - " << students[i].age << endl;
    }

    delete[] students;

    return 0;
}

Output:

Enter the number of students: 2
Enter name and age for student 1: coder
15
Enter name and age for student 2: programmer
18
Student 1: Name - coder, Age - 15
Student 2: Name - programmer, Age - 18

Explanation:

• User Input: The user enters the number of students they want to manage.
• Dynamic Allocation: Memory is dynamically allocated for an array of Student objects based on the user’s input.
• Data Input: The user inputs the name and age of each student in the array.
• Data Display: The program displays the stored information for each student.
• Memory Release: After data processing, the allocated memory is released using delete[] to prevent memory leaks.

A Problem to Solve

Problem Statement:

You are given the task of creating a simple student record system that stores the names and grades of students in a class. The class size is not fixed and can vary. Your program should use dynamic memory allocation to manage the memory used for these records efficiently.

Requirements:

1. Input the Class Size: Prompt the user to enter the number of students in the class.
2. Allocate Memory for Student Records: Use dynamic memory allocation (new) to create space for the student records. A student record consists of a name (string) and a grade (integer).
3. Input Student Records: Prompt the user to enter the name and grade for each student. Store this information in the allocated memory.
4. Calculate and Display the Average Grade: Calculate the average grade of the students and display it to the user.
5. Find the Top Student: Find and display the name and grade of the student with the highest grade.
6. Deallocate Memory: After all processing, make sure to release the dynamically allocated memory using the delete operator.

Constraints:

• The number of students in the class is at least 1 and at most 1000.
• The name of a student is a non-empty string containing at most 50 characters.
• The grade of a student is an integer between 0 and 100.

Hints:

• You might want to define a struct to represent a student record.
• Consider using the new operator to dynamically allocate an array of student records.
• Don’t forget to use the delete operator to deallocate the memory once you’re done.

Example:

Enter the number of students: 3
Enter name and grade for student 1: Alice 90
Enter name and grade for student 2: Bob 85
Enter name and grade for student 3: Charlie 95

Average Grade: 90
Top Student: Charlie with grade 95

Understand By Table

Examples of Using Dynamic Memory Allocation in C++

Let’s look at some examples to see how dynamic memory allocation can be used in C++. We’ll provide the code, the expected output, and a step-by-step explanation of how dynamic memory allocation is used.

Example 1

#include
using namespace std;
int main() {
    int* ptr = new int;
    *ptr = 5;
    cout << *ptr << endl;
    delete ptr;
    return 0;
}

Output:

5

Explanation: In this example, we’re using dynamic memory allocation to create an integer in memory, assign the value 5 to it, print it, and then delete it.

Example 2

#include
using namespace std;
int main() {
    int* arr = new int[3];
    arr[0] = 1;
    arr[1] = 2;
    arr[2] = 3;
    for(int i = 0; i < 3; i++) {
        cout << arr[i] << " ";
    }
    delete[] arr;
    return 0;


}

Output:

1 2 3 

Explanation: Here, we’re using dynamic memory allocation to create an array of integers in memory, assign values to it, print the values, and then delete the array.

Example 3

#include
using namespace std;
int main() {
    int size;
    cout << "Enter the number of elements: ";
    cin >> size;
    int* arr = new int[size];
    for(int i = 0; i < size; i++) {
        arr[i] = i+1;
    }
    for(int i = 0; i < size; i++) {
        cout << arr[i] << " ";
    }
    delete[] arr;
    return 0;
}

Output:

Enter the number of elements: 12
1 2 3 4 5 6 7 8 9 10 11 12 

Explanation: In this example, we’re using dynamic memory allocation to create an array of a user-defined size, assign values to it, print the values, and then delete the array.

The Pros and Cons of Using Dynamic Memory Allocation

Key Takeaways

• Dynamic memory allocation in C++ optimizes memory usage.
• It allows us to reserve memory space during program execution.
• Memory can be released after it is no longer needed.
• Provides flexibility in managing data structures.
• Helps avoid unnecessary memory usage.
• It enables efficient use of memory resources.
• Can make programs more efficient and flexible.

Conclusion

In conclusion, dynamic memory allocation is a powerful tool in C++. By understanding how to use dynamic memory allocation, you can write better, more efficient programs. So keep practicing, and soon you’ll be a pro at using dynamic memory allocation!

FAQs

• What is dynamic memory allocation in C++?
  Dynamic memory allocation in C++ is a process by which the size of a data structure (like an array) can be changed during the runtime.
• Why do we use dynamic memory allocation in C++?
  We use dynamic memory allocation in C++ to optimize our use of memory. It allows us to reserve memory space during the execution of the program and release it after we’re done using it.
• How do we use dynamic memory allocation in C++?
  We use dynamic memory allocation in C++ by using the ‘new’ keyword to allocate memory and the ‘delete’ keyword to release memory.
• Can using dynamic memory allocation make code more confusing?
  Yes, if not used correctly, dynamic memory allocation can lead to memory leaks and other problems. It’s important to understand how dynamic memory allocation works and when to use it.
• What are some examples of using dynamic memory allocation in C++?
  Some examples include creating a single variable or an array in memory, assigning values to it, and then deleting it.