Basics of Dynamic Memory Allocation - YouTube

Here in this presentation, we will discuss

some of the basics of dynamic memory allocation.

So, let's get started.

First we will discuss about static memory allocation.

Then we will move to dynamic memory allocation.

Memory allocated during compile time is called static memory.

It should be very clear that the memory allocated

during compilation time, or the time when the programmer is creating

the program is called static memory.

And the memory allocated is fixed and cannot be

increased or decreased during run time.

If you run the program, obviously the memory, which has

been allocated at compile time, is fixed and

cannot be increased or decreased.

For example, here You can see that we have an array,

which consists of five elements.

Although you can see over here

that the size is fixed.

So, memory is allocated at compile time.

and obviously, here the size is fixed.

The programmer has fixed this size,

and we cannot increase this size or decrease the size at runtime.

It should be very clear.

Now, there are certain problems which

we faced in static memory allocation.

If you are allocating memory for an array during compile time,

then you have to fix the size at the time of declaration.

Obviously, there is least flexibility because you have to then you have to fix the size at the time of declaration.

Obviously, there is least flexibility because you have to

fix the size at the time of declaration itself.

Size is fixed and user cannot increase or decrease

the size of the array at run time.

This size is fixed. User cannot increase or decrease the size

of the array, or any object at run time.

If the value stored by the user in the array at run time is less

than the size specified, then there will be wastage of memory.

Let me tell you that, here I'm talking about array.

It could be any object, right?

So, if the value stored by the user in the array at run time is

less than the size specified, if the user enter elements

less than the size specified, then

obviously there will be a wastage of memory

If the value stored by the user in the array at run time

is more than the size specified.

If he or she enters more elements in the array,

then obviously the program may crash or misbehave.

This is also a possibility, right?

Now, here comes someone to rescue.

The one who can solve the problem is dynamic memory allocation.

The process of allocating memory at the time of execution

is called dynamic memory allocation.

It should be very clear that the process of allocating

memory at the time of execution is called dynamic memory allocation.

You are allocating memory at run time.

So, user has the flexibility.

He or she can allocate memory

according to his or her needs, right?

You might have remembered this diagram

from C programming lectures.

This is nothing but a memory layout of C program.

These are the different memory segments.

The one which we will talk about here

is the heap memory segment.

Heap is the segment of memory,

where dynamic memory allocation takes place.

Unlike stack, where memory is allocated

or deallocated in a defined order,

heap is an area of memory where memory is allocated

or deallocated without any order or randomly.

In stack, everything is defined in order.

You have to enter elements at

the top of the stack, you have to delete elements

from the top of the stack.

Everything is well defined and everything is in the order.

So, memory is allocated or deallocated

in a defined order in case of stack.

But in case of heap, there is no restriction as such.

Memory is allocated or deallocated without any order or randomly.

There are certain built-in functions that can help

in allocating or deallocating some memory space at run time.

It is interesting because, you know,

there are certain built-in functions available

that can help us in allocating

or deallocating some memory space at run time in heap.

Before revealing those functions, I would like to

discuss one very important point.

Pointers play a very important role in dynamic memory allocation.

And this is one such application of pointers.

Allocated memory can only be accessed through pointers.

The only possible way which we can access

he memory allocated dynamically is through pointers.

Now, here are certain built-in functions that I was talking about.

malloc(), calloc(), realloc(), and free().

These are the built-in functions which

are used to allocate or deallocate memory dynamically.

We will discuss all these functions

in the subsequent lectures.

Okay friends.

This is it for now.

Thank you for watching this presentation.