Dynamic memory allocation

memory_allocation_in_cpp


Dynamic memory allocation in C++ allows the program to allocate memory during runtime, which is especially useful when the size of the data structure isn’t known in advance. Using new and delete, we can manage memory manually, creating and releasing memory on the heap as needed. Let’s break down how dynamic memory allocation works, memory management basics, and the concept of pointers to pointers.

Dynamic Memory Allocation with new and delete

In C++, new is used to allocate memory on the heap, and delete is used to release that memory. This is essential for managing resources effectively, especially when creating objects or arrays whose sizes can vary at runtime.

  • new Operator: Allocates memory on the heap and returns a pointer to it.
  • delete Operator: Frees the memory previously allocated by new.

Example: Allocating and deleting a single integer dynamically.

Dynamic_memory_allocation

In this example:

  • We allocate memory for an integer using new int and store the address in ptr.
  • We assign a value to *ptr, which is the memory pointed to by ptr.
  • We then release the memory with delete ptr and set ptr to nullptr to avoid accidental use.

Dynamic Arrays with new and delete[]

When working with arrays whose size is determined at runtime, new allows us to allocate arrays dynamically. We use delete[] to release the entire array from memory.

Example: Allocating and deleting a dynamic array.

Dynamic_array

Here:

  • We allocate an array of integers with a size defined by user input.
  • We release the memory with delete[] arr to free the entire array.

Memory Management Best Practices

Proper memory management is crucial in C++ to avoid issues like memory leaks and dangling pointers:

  • Always release memory: Use delete or delete[] after you’re done with dynamically allocated memory.
  • Avoid multiple deletions: Deleting the same pointer twice can cause undefined behavior.
  • Nullify pointers after deletion: Setting a pointer to nullptr after deletion helps prevent accidental access to freed memory.


Pointers to Pointers

A pointer to a pointer is a pointer variable that holds the address of another pointer. This concept is often used in multi-dimensional dynamic arrays and when passing pointers to functions.

Syntax:

pointer_to_pointer


Example: Basic pointer-to-pointer usage.

pointer_to_pointer

In this example:

  • ptr holds the address of value.
  • ptrToPtr holds the address of ptr.
  • **ptrToPtr gives us the original value by dereferencing twice.

Dynamic Multi-Dimensional Arrays with Pointers to Pointers

Using pointers to pointers, we can create dynamic multi-dimensional arrays. This is useful when the number of rows and columns may vary at runtime.

Example: Creating a dynamic 2D array.

Dynamic_multi_array

In this example:

  • We first allocate memory for rows as an array of int*.
  • For each row, we allocate memory for cols elements, effectively creating a 2D array.
  • We release memory row by row and then delete the row pointers to avoid memory leaks.

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