Basics of Dynamic Memory Allocation

Summary

This presentation explores the fundamentals of dynamic memory allocation, contrasting it with static memory allocation. Static memory, allocated at compile time, is fixed and lacks flexibility, leading to potential memory wastage or program crashes if the allocated size doesn't match runtime needs. Dynamic memory allocation, on the other hand, offers runtime flexibility, allowing memory to be allocated and deallocated as needed without a predefined order. The heap memory segment is highlighted as the area for dynamic allocation, and built-in functions like malloc(), calloc(), realloc(), and free() are introduced as essential tools for managing memory dynamically. Pointers are emphasized as crucial for accessing dynamically allocated memory.

Takeaways

• 📚 The presentation introduces the concepts of static and dynamic memory allocation.
• 🔒 Static memory allocation is fixed at compile time and cannot be changed during runtime.
• 🗄️ An example of static allocation is an array with a fixed size set by the programmer.
• 🚫 Limitations of static memory include inflexibility and potential memory wastage if the allocated size doesn't match runtime needs.
• 🔄 Dynamic memory allocation allows memory to be allocated and deallocated during runtime, providing more flexibility.
• 🧩 The heap memory segment is where dynamic memory allocation occurs, contrasting with the stack's ordered allocation.
• 🔑 Pointers are crucial for accessing dynamically allocated memory, as they are the only way to reference it.
• 🛠️ Built-in functions like malloc(), calloc(), realloc(), and free() are used for dynamic memory management.
• 📈 Dynamic allocation enables users to allocate memory according to their needs, which can improve memory usage efficiency.
• ⏭️ The presentation promises to delve deeper into the specifics of dynamic memory allocation functions in future lectures.

Q & A

What is static memory allocation?

Static memory allocation refers to the allocation of memory during compile time. The memory size is fixed and cannot be increased or decreased during runtime.

What are the limitations of static memory allocation?

The main limitations of static memory allocation are the lack of flexibility, fixed memory size at declaration, potential memory wastage if less space is used, and program crashes or misbehavior if more space is needed than allocated.

Can you provide an example of static memory allocation?

An example of static memory allocation is defining an array of fixed size, such as an array of 5 elements. The size is set at compile time and cannot be changed at runtime.

What is dynamic memory allocation?

Dynamic memory allocation is the process of allocating memory during runtime, allowing the program to allocate memory as needed and providing flexibility to increase or decrease memory size during execution.

What are the advantages of dynamic memory allocation over static memory allocation?

Dynamic memory allocation offers flexibility, as memory can be allocated or deallocated as needed during execution. This avoids memory wastage and potential program crashes due to insufficient or excessive allocation.

What is the role of the heap in dynamic memory allocation?

The heap is the memory segment where dynamic memory allocation occurs. Unlike the stack, memory in the heap is allocated and deallocated without any specific order.

How is memory allocated or deallocated in the stack?

In the stack, memory is allocated and deallocated in a defined order, with memory being added and removed in a last-in, first-out (LIFO) manner. This strict order is not present in the heap.

Why are pointers important in dynamic memory allocation?

Pointers are crucial in dynamic memory allocation because they are the only way to access memory that has been allocated dynamically. Without pointers, the allocated memory cannot be used.

What built-in functions are used for dynamic memory allocation?

The built-in functions used for dynamic memory allocation are `malloc()`, `calloc()`, `realloc()`, and `free()`. These functions help allocate and deallocate memory during runtime.

What will be covered in the subsequent lectures mentioned in the script?

The subsequent lectures will cover the use and functionality of `malloc()`, `calloc()`, `realloc()`, and `free()` functions in detail for dynamic memory allocation.

Outlines

00:00

📖 Introduction to Memory Allocation

This paragraph introduces the topic of memory allocation, starting with a discussion on static memory allocation. It explains how memory allocated during compile time is fixed and cannot be modified during runtime. The speaker highlights the limitations of static memory allocation, including the inability to increase or decrease memory size at runtime and the potential for memory wastage or program crashes when the allocated size is either too large or too small for the user's input.

🚧 Problems with Static Memory Allocation

The paragraph dives into the specific issues encountered with static memory allocation. It emphasizes the lack of flexibility, as the size of memory must be determined during compile time, making it challenging to adapt to runtime needs. If less memory is used than allocated, it results in memory wastage, while exceeding the allocated memory size could lead to program crashes. These limitations are clearly highlighted with examples.

🛠️ Dynamic Memory Allocation to the Rescue

This section introduces dynamic memory allocation as a solution to the problems of static memory allocation. Unlike static allocation, dynamic memory allows memory to be allocated at runtime, giving the user the flexibility to allocate memory based on actual requirements. The speaker also mentions how dynamic memory allocation happens in the heap memory segment, contrasting it with stack memory, which follows a strict order of allocation and deallocation.

🏗️ Memory Segments and the Heap

This paragraph explains the different memory segments in a C program, focusing on the heap, where dynamic memory allocation occurs. It contrasts heap memory with stack memory, explaining that while stack follows an ordered allocation and deallocation process, heap memory is allocated and deallocated randomly, providing greater flexibility. The speaker emphasizes how this unordered process makes heap memory suitable for dynamic memory allocation.

🔧 Key Functions for Dynamic Memory Allocation

The speaker introduces several important built-in functions for dynamic memory allocation: `malloc()`, `calloc()`, `realloc()`, and `free()`. These functions are crucial for allocating and deallocating memory in the heap during runtime. Additionally, the paragraph emphasizes the role of pointers in accessing dynamically allocated memory, highlighting how pointers are essential in managing memory allocated through these functions.

👋 Conclusion and Preview

In this closing paragraph, the speaker wraps up the discussion on dynamic memory allocation and hints at more detailed explanations of the functions `malloc()`, `calloc()`, `realloc()`, and `free()` in upcoming lectures. The presentation concludes with a thank you message to the viewers.

Keywords

💡Static Memory Allocation

Static memory allocation refers to memory that is allocated during the compile time of a program. Once allocated, the memory size is fixed and cannot be changed during runtime. In the video, static memory is exemplified by an array with a fixed size, which cannot be adjusted later, leading to potential problems like memory wastage or crashes if the size is inadequate.

💡Dynamic Memory Allocation

Dynamic memory allocation is the process of allocating memory at runtime, providing flexibility to allocate or free memory as needed. Unlike static memory, dynamic memory can grow or shrink based on the program’s requirements. The video presents dynamic memory allocation as a solution to the limitations of static memory allocation, allowing users to handle memory more efficiently.

💡Array

An array is a collection of elements, typically of the same type, stored in contiguous memory locations. In the video, the array is used to demonstrate static memory allocation, where its size must be defined at compile time. The limitations of fixed-size arrays are highlighted, such as memory wastage if fewer elements are stored or program failure if more elements are added than specified.

💡Heap

The heap is a segment of memory where dynamic memory allocation occurs. Memory in the heap can be allocated and deallocated in any order, unlike the stack, which follows a structured approach. The video mentions heap memory as the primary area for dynamic memory allocation and contrasts it with the stack’s organized allocation.

💡Stack

The stack is a region of memory where data is allocated and deallocated in a specific order—last-in, first-out (LIFO). The video explains how memory allocation in the stack is sequential and ordered, in contrast to the heap, where memory management is more flexible and unordered.

💡Malloc()

Malloc (memory allocation) is a built-in function in C that allocates a specified amount of memory during runtime and returns a pointer to it. The video introduces malloc() as one of the key functions used for dynamic memory allocation in the heap, which can help solve the limitations of static memory.

💡Calloc()

Calloc (contiguous allocation) is another function used for dynamic memory allocation, similar to malloc(), but it also initializes the allocated memory to zero. The video introduces calloc() as an important function to manage memory allocation dynamically, providing more flexibility compared to static memory.

💡Realloc()

Realloc (re-allocation) is a function used to resize previously allocated memory blocks. The video highlights realloc() as a function that allows programmers to adjust the size of dynamically allocated memory as needed during runtime, thus avoiding memory wastage or overflow.

💡Free()

Free is a function that deallocates memory previously allocated with malloc(), calloc(), or realloc(). The video explains that free() is crucial for preventing memory leaks by releasing memory back to the heap once it is no longer needed, ensuring efficient memory management in dynamic allocation.

💡Pointers

Pointers are variables that store the memory addresses of other variables. In the context of dynamic memory allocation, pointers are essential because dynamically allocated memory can only be accessed via pointers. The video emphasizes the importance of pointers in managing memory, particularly when using functions like malloc() and free().

Highlights

Introduction to dynamic memory allocation and its basics.

Static memory allocation occurs during compile time, with fixed memory that cannot be altered during runtime.

Static memory allocation limits flexibility as size must be declared during compilation, making it unchangeable during runtime.

Issues with static memory allocation include potential memory wastage if the allocated size is not fully utilized.

If the user inputs more elements than the static array's size, the program may crash or behave unexpectedly.

Dynamic memory allocation allows memory to be allocated at runtime, providing greater flexibility.

Dynamic memory allocation occurs in the heap memory segment, unlike stack memory, which follows a defined order.

Heap memory allows allocation and deallocation without a defined order, making it more flexible than stack memory.

Pointers are crucial in dynamic memory allocation as they are the only way to access dynamically allocated memory.

Key built-in functions for dynamic memory management include malloc(), calloc(), realloc(), and free().

malloc() function allocates a specified amount of memory in the heap.

calloc() function allocates memory for an array of elements and initializes them to zero.

realloc() function resizes previously allocated memory blocks without losing the data.

free() function deallocates memory previously allocated by malloc(), calloc(), or realloc().

The presentation concludes by noting the importance of understanding memory allocation functions for efficient programming.

Transcripts

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.