new keyword¶

Notes¶

The new keyword is C++ equivalent of malloc() from C along with the added benefit of calling the constructor when used with a class. Using new allows you to allocate memory on Heap.

How the new keyword works?¶

On calling new, the new keyword takes the size needed to be loaded in the memory as input.
It searches through the heap to find a continuous block of memory as required.
After successfully finding the block of memory, it returns the pointer to the memory.

How to load a variable on heap?¶

int *var = new int;

The var will store the pointer to the heap memory where the value can be stored. It will be of 4 bytes. (size of int = 4 bytes)

How to load a block of memory?¶

int *b = new int[50]; //200 bytes

Using [] brackets will allocate 50 block of memory with the size of int. This will be 200 bytes. (50 blocks of size of int = 50 x 4 = 200 bytes)

Important Things to know before using new¶

Always clear the memory after the scope of new is complete. Since the memory is allocated in heap, it does not auto delete. Clear the memory using delete keyword as follows:

int *a = new int;
delete a;//Since A single block of memory is allocated//clear directly using delete keyword

int *b = new int[50];
delete[] b;// Remember to use [] next to delete if you want to clear all the memory blocks.// If you don't use [], it will only clear the first block of memory

For a class, though new in C++ it equivalent to malloc in C, do not use them interchangeably. malloc() just returns pointer to the memory block when you use it with a class. new returns the pointer and also initializes the object for the class.