C_80 Void Pointer in C | Detailed explanation with program

Summary

This video script delves into the concept of void pointers in C programming. It explains that a void pointer, akin to an empty glass that can be filled with any liquid, is a generic pointer without an associated data type. The script teaches how to declare and use void pointers, emphasizing the need for type casting when dereferencing to access values of different data types. The practical demonstration shows using a single void pointer to access variables of various types, highlighting its utility in simplifying code and handling dynamic memory allocation.

Takeaways

• 😀 The video discusses special pointers in C programming, focusing on void pointers.
• 🔍 A void pointer in C is a generic pointer that has no associated data type, similar to an empty glass that can be filled with any liquid.
• 📚 The term 'void' generally means 'empty' or 'nothing', and a void pointer is used to point to any data type.
• 💡 Declaring a void pointer involves using the 'void' keyword in the pointer declaration, such as `void *vp;`.
• 🚫 A void pointer cannot be dereferenced directly; it must be typecast to a specific data type before being used.
• 🔄 The flexibility of a void pointer allows it to be converted into any other pointer type, making it useful for various programming scenarios.
• 💻 The video demonstrates how to use a void pointer in a program, showing how it can store the address of different data types like int, float, and char.
• 🔑 Typecasting a void pointer is essential for accessing the value it points to, as the compiler needs to know the data type to correctly interpret the memory.
• 📈 The practical use of void pointers is highlighted in the video, showing how they can be used to access multiple data types with a single pointer.
• 🔍 The video also mentions that void pointers are used in dynamic memory allocation functions like malloc and calloc, which return void pointers to the allocated memory.

Q & A

What is a void pointer in C?

A void pointer in C is a pointer that has no associated data type. It is essentially a generic pointer that can point to any data type. It is declared using the 'void' keyword and can be typecast to any other pointer type.

Why are void pointers useful in programming?

Void pointers are useful because they can be used as a generic pointer to any data type. This allows a single pointer to be used to access different data types, which can be convenient in situations like dynamic memory allocation where the data type is not known at compile time.

How do you declare a void pointer in C?

A void pointer is declared in C using the 'void' keyword followed by an asterisk and the pointer name. For example, `void *vp;` declares a void pointer named 'vp'.

Can you directly dereference a void pointer?

No, you cannot directly dereference a void pointer. Before dereferencing, you must typecast the void pointer to the appropriate data type pointer (e.g., `int *`, `float *`, `char *`) to ensure the compiler knows how many bytes to access.

What is the significance of the term 'void' in the context of a void pointer?

The term 'void' in the context of a void pointer signifies that the pointer does not have an associated data type. It can be thought of as an 'empty' or 'generic' pointer that can be filled with any type of data.

How does a void pointer differ from other pointers like integer pointer, float pointer, or character pointer?

A void pointer differs from other pointers in that it does not have a specific data type associated with it. Other pointers, such as integer pointers (`int *`), float pointers (`float *`), or character pointers (`char *`), are associated with specific data types and can only point to variables of those types.

What is the purpose of typecasting a void pointer?

Typecasting a void pointer is necessary to specify the data type of the variable it points to. This is required before dereferencing the pointer so that the compiler knows how many bytes to access and can correctly interpret the data.

Can a void pointer store the address of any variable?

Yes, a void pointer can store the address of any variable, regardless of its data type. However, before accessing the data at that address, the void pointer must be typecast to the appropriate pointer type corresponding to the data type of the variable.

What are some common uses of void pointers in C?

Void pointers are commonly used in situations where the data type is not known until runtime, such as in dynamic memory allocation with functions like `malloc` and `calloc`. They are also used in generic functions or APIs where the function needs to handle data of various types.

How does the concept of a void pointer relate to dynamic memory allocation in C?

In C, functions like `malloc` and `calloc` return a void pointer. This void pointer is then typecast to the appropriate pointer type by the programmer to store and access dynamically allocated memory. This allows for flexible memory management where the data type can be specified at runtime.

Outlines

00:00

📚 Introduction to Special Pointers in C

This paragraph introduces the concept of special pointers in C programming. The speaker discusses various types of pointers such as word pointer, generic pointer, null pointer, and dangling pointer. The focus is on void pointers, explaining what they are, their purpose, and how they are used. The void pointer is described as a type of pointer that does not have an associated data type, making it versatile for various uses. The speaker also mentions that they will demonstrate the use of void pointers with practical examples on their laptop.

05:00

🔍 Understanding and Using Void Pointers

The speaker delves deeper into void pointers, explaining that they are essentially pointers without a specific data type. They use the analogy of an empty glass that can be filled with any liquid to illustrate the concept. The paragraph covers how to declare a void pointer and how it can be converted into any other type of pointer through type casting. The speaker emphasizes the need for type casting when dereferencing a void pointer, as the compiler needs to know the data type to correctly access the memory. An example is given where the void pointer is assigned the address of an integer variable, and the speaker explains the error that occurs when trying to dereference it without type casting.

10:02

🔄 Type Casting and Practical Use of Void Pointers

This paragraph discusses the practical applications of void pointers, highlighting their utility in accessing different data types with a single pointer. The speaker explains that while void pointers do not have an associated data type, they can be type cast into any other pointer type, allowing for flexibility in accessing various data types. Examples are provided where the void pointer is used to access integer, float, and character variables, demonstrating how a single void pointer can be used to handle multiple data types. The speaker also mentions the use of void pointers in dynamic memory allocation functions like malloc and calloc, which return void pointers.

15:15

💻 Demonstrating Void Pointers in Code

The speaker presents a practical demonstration of using void pointers in C code. They create a file named 'void pointer do c' and declare a single void pointer. The code example shows how the void pointer is used to access variables of different data types (integer, float, and character) by first storing their addresses and then dereferencing the pointer after type casting. The speaker runs the code to show that the values of the variables can be accessed correctly using the void pointer, emphasizing the benefit of using a single pointer to handle multiple data types.

Keywords

💡Pointers

Pointers are a fundamental concept in C programming, allowing programmers to manipulate memory addresses. In the video, pointers are introduced as variables that store the memory address of other variables. They are essential for dynamic memory allocation and accessing data stored at specific locations in memory.

💡Void Pointer

A void pointer in C is a generic pointer type that does not have an associated data type. It can point to any data type, making it versatile for various operations. The video explains that a void pointer is like an 'empty glass' that can be filled with any type of data, emphasizing its flexibility.

💡Data Type

Data types in programming define the kind of data a variable can hold, such as integers, floats, or characters. The video discusses how pointers, like void pointers, can be associated with different data types, which is crucial for understanding how they can be used to access and manipulate data in memory.

💡Type Casting

Type casting is the process of converting one data type to another. In the context of void pointers, type casting is necessary to specify the data type when dereferencing the pointer. The video demonstrates how to cast a void pointer to an integer pointer, a float pointer, or a character pointer to access the correct data type.

💡Dangling Pointer

A dangling pointer is a pointer that points to a memory location that has been freed or is otherwise invalid. While not extensively discussed in the script, the concept is mentioned as one of the special pointers that will be covered in later videos, indicating the importance of managing pointers carefully.

💡Null Pointer

A null pointer is a pointer that does not point to any valid memory location. It is often used to indicate the absence of a valid address. The video script mentions null pointers as a type of special pointer that will be discussed in subsequent videos, highlighting the need to understand different pointer behaviors.

💡Generic Pointer

While not explicitly defined in the script, the term 'generic pointer' could be inferred to refer to a pointer that can handle multiple data types, similar to a void pointer. The video emphasizes the versatility of void pointers, which can be seen as a form of generic pointer.

💡Memory Address

Memory addresses are unique identifiers for locations in a computer's memory where data is stored. The video script frequently refers to memory addresses when discussing pointers, as pointers store these addresses to access and manipulate the data stored at those locations.

💡Dereferencing

Dereferencing a pointer involves accessing the data stored at the memory address the pointer holds. The video explains that dereferencing a void pointer requires type casting because the compiler needs to know the data type to correctly access the appropriate amount of memory.

💡Dynamic Memory Allocation

Dynamic memory allocation refers to the process of allocating memory during runtime, typically using functions like malloc and calloc in C. The video mentions that these functions return void pointers, which can be used to access the allocated memory, demonstrating the practical application of void pointers.

💡Compiler

The compiler is a software tool that translates source code into machine code. In the context of the video, the compiler's role is highlighted in understanding how it uses data types associated with pointers to determine how much memory to access when dereferencing.

Highlights

Introduction to special pointers in C programming, including void pointer, word pointer, generic pointer, null pointer, and dangling pointer.

Void pointer is a generic pointer type that can point to any data type.

Void pointer has no associated data type, making it versatile for various uses.

Void pointer can be converted into any other pointer type through type casting.

Declaration of a void pointer involves using the 'void' keyword.

Demonstration of how to declare and use a void pointer in a program.

Explanation of why void pointers cannot be dereferenced directly.

Void pointers require type casting before dereferencing to specify the data type.

Illustration of accessing an integer variable using a void pointer by type casting it to an integer pointer.

Example of accessing a float variable using a void pointer by type casting it to a float pointer.

Demonstration of accessing a character variable using a void pointer by type casting it to a character pointer.

Void pointers are used in dynamic memory allocation functions like malloc and calloc.

Practical example of using a void pointer to access variables of different data types in a single program.

Void pointers allow for accessing multiple data types with a single pointer, reducing the need for multiple pointers.

Explanation of the practical applications and benefits of using void pointers in programming.

Void pointers are essential in scenarios where the data type is unknown or needs to be flexible.

Final demonstration of accessing and printing values of different data types using a single void pointer in a C program.

Transcripts

so in the series of learning programming

in c we are discussing pointers in C in

pointers also there are some special

pointers like word pointer generic

pointer null pointer dangling pointer

and these pointers are also very helpful

right so we are going to discuss these

pointers one by one in this video I'll

discuss void pointer everything about

void pointer like what is void pointer

the need of void pointer why we use void

pointer how to declare this pointer how

to use this pointer right with the help

of a program right and I'll show you

that program also on my laptop practical

also we'll see right everything we'll

discuss about this pointer in this video

and one by one by one in later videos

you will discuss dangling pointer null

pointer all the these special pointers

we'll discuss right so you'll also see

how this pointer is different from the

other pointers we have discussed like

integer pointer character pointer float

pointer everything about this pointer we

will discuss in this video every single

detail right so now let's discuss what

is void pointer I hope you know the

meaning of this void in general term in

English term like K or empty right so

it's like if there's a glass and that is

empty that is void you can fill that

glass with maybe water with some other

drink or with milk anything you can you

know put in that glass right so apply

the same concept here also try to relate

that thing void pointer means this

pointer is of void type means this

pointer is having no Associated data

type if you will see the definition it

that maybe on internet or in any book

then you must you must uh see that word

pointer is what it is not having any

Associated data type that is in simple

terms that is a the same example you can

take an empty glass you can fill that

glass with either you know with water or

with milk or with some other drink or

anything right so same this pointer is

having no Associated data type with it

so you can convert this pointer in any

other pointer also now whatever I am

saying what's the meaning of that thing

see first of all if I write a pointer

something like this int

star

P one is float star FP here I'm writing

IP or here I'm writing

CP it means there are three pointers

this is integer pointer see data type of

pointer is not integer it means IP is a

pointer which is pointing to

a int data type or maybe this is storing

an address of a variable whose data type

is integer or simply we call it as in

integer pointer or pointer to integer

this is float pointer or you can say a

pointer to float this is pointer to

character right so they they are having

their Associated data type the data type

of this is the data type which is

associated with this pointer is int with

this float with this care but word

pointer is having no Associated data

type so how to declare this pointer see

the synx is same obviously if it is a

pointer you have to use EST this will

tell that it is a pointer name here you

will write pointer name suppose I'm

writing pointer name word pointer that

is WEP so what you will write here at

the place of this data type simply we

will write what this void this keyword

void so this this is what a declaration

of void pointer right I hope you

understand what is void pointer it is it

it is not having any Associated data

type right so you can convert it into

any other data type you can type cast it

right here it means this can store

address of a variable like if a address

variable is in a another variable I'm

taking float B one variable I'm taking

care

C so this pointer can store IP is equal

to address of

a only this is possible this can store

address of a only if you write IP is

equal to address of B this would be

wrong and what if we can write FP is

equal to address of B and this pointer

CP is equal to address of

C right but here this pointer can store

address of

this int variable also float variable

also care variable

also right so it's like a generic

pointer same in Empty Glass we can fill

maybe water some other drink or maybe

milk anything we can typ cast it so we

can typ cast this pointer for that you

have to typ cast this pointer directly

if you write suppose here I'm writing

VP is equal to address of

a it means now this word pointer is

storing address of

this variable a and suppose in a I'm

having a is equal to 5 but if you will

print like print F percentage D and

whatever in a I want to print in a I

have five and this WEP this

pointer this is pointer

this is pointing to a suppose address is

th000 so in VP we have address of a that

is

1,000 so if you want to access this

using this wordid pointer what you will

write D reference you will D reference

this pointer I hope you know this

because we have discussed these Concepts

I know uh in our previous videos of

pointers right it means estri VP value

at this address here we have th so so it

should give

five but it is wrong you cannot

dreference aoid pointer it will give you

error first of all you have to typ cast

it because see when you deference then

it will see suppose I'm D referencing

this IP I'm writing here IP IP is equal

to address of a suppose this is not VP

this is IP this pointer right

and EST IP so it will give you five this

is correct because this is integer

pointer this is not word pointer so now

when you dreference it it means compiler

now know add the data type of this

pointer the associated data type with

this pointer is integer means now

compiler know in modern compiler

obviously it depends on machine to

machine but I take like in modern

compiler integer take four bytes so now

compiler

[Music]

know 1 2 3 4 suppose in memory within

these four bytes this a the value has

been stored five converted into binary

form like 32 bits and then this five has

been stored here and address of first

bite is 1,000 then 1,1 1, and2 1,

and3 something like this right so

now value at this address address is

th000 address is th000 so now from here

we want to access now Associated data

type is integer so when you apply D

referencing now the compiler know

that he has to access four bytes 1 2 34

because data type is

integer that is why the data type is

needed when you dreference that pointer

right so now it will access four

bytes and it will give you

value same if you access D reference

this character pointer character will

take one bite so now compiler know by

seeing this data type compiler will know

that he has to access only one by

because dat type is

character right same float if float is

there means four bytes so it has to

access four bytes but here we are using

suppose

VP now word is what it is not a data

type now how compiler will know

that it has to access one byte or 4 byte

or how many bytes compiler doesn't know

so how to access this void pointer how

to dreference this void pointer how to

get the

value right value may be within one by

or value may be in four bytes don't know

it is void pointer right that is why we

we cannot dreference this word pointer I

hope you got the reason why you cannot

dreference this word pointer right if

not then you can ask me in comment box

maybe in maybe in another video I can

tell you the process in a separate video

right so now that is why it will give

error so first of all we will have to

typ cast this

one typ cast means now I'm storing in VP

address of a so here we have VP I'm

storing address of a and data type of

this is what integer so we have to typ

cast it into integer pointer so now how

to type cast it here rather than using

this what you will

write int

estri VP so first this word pointer

would be typ casted or you can say

converted into an integer pointer and

now we apply this D referencing

operator right now it will give you what

value

five because now now we have converted

into int or we you can say typ casted

into integer pointer so now compiler

know if int then it has to access four

bytes so data would be in four bytes so

starting by is this so it will access

1,00,000

1,2,3 till 103 4 bytes and obviously

this is integer type and this would be

stored in four bytes only so definitely

you will get five

right now if I write if I write

something like this VP is equal to

address

of CP uh sorry address of uh

C I'm storing VP this address variable

is what character type right so here in

C suppose I'm storing character is uh

zero yeah 0 is character it's not like

that AB BCD is only character whatever

you will write in single code that will

be in character A Single Character you

can write so if you write zero here so

zero would be considered as a character

right so now address of C now VP is

suppose here we have this is C here we

have zero obviously in that form like in

uh Zer and one form that would be stored

right and now VP this is a pointer and

this is pointing to here suppose address

is 2,000 so it we are storing 2000

now now how to

print how to print this is character we

know this is character so we'll use

percentage C estri first type

cast type cast into a character pointer

so we'll write here care s and now name

is

VP that's it first of all it will be typ

casted into character pointer and then

we'll der reference it so D reference

means value at this point value is what

zero so it will give zero I hope you got

this and if you write here VP is equal

to address of float variable so before

printing type cast into float and that

it will print floating value suppose in

B I have 1.11 so it will print

1.11

right so simple point about word pointer

there is nothing much about word pointer

it is not having an data type you can

convert it into any other pointer or you

can typ cast it into any other pointer

right so now what's the use maybe you

think that rather than typ casting

obviously ultimately we have to typ cast

it so rather than this directly use an

INT pointer and directly deference that

pointer what's the use of using this

void pointer so here if in the same

program same program if I'm using this

int also float also so care

also so we have to declare three

pointers one is for INT one is for float

one is for

character but if you use this word

pointer no need to declare these

pointers you can access all these three

values using single pointer word pointer

only a single pointer how I know I I I

hope you know the

answer first store the address of a type

card it and print then assign in this

address of B while printing type cast it

then assign address of C while printing

type cast it and you can print you can

access all the three values three values

of different different data

types so here we are using only one

pointer we are using only one pointer

and we are accessing values of three you

can say data types integer also float

also car also one more thing when we use

Melo and

kello we'll also discuss these

things these are built-in function for

dynamic memory allocation so they return

what void

pointer right when they assign they

return memory like they return word

pointer to that memory so in that memory

we can store any uh value like integer

also float also character also right so

there also these void pointers would be

used right in Malo and

kog so that also discuss when we discuss

dynamic memory location these are

Advanced you know Concepts and see right

so that is why we use I guess uh word

pointer you you are clear with what is

word pointer why we use word pointer

like and you can say what's the need of

word pointer now let me show you know

practically we'll write down some code

and we'll see use of word pointer right

so now let me create a file here

I'm taking name void pointer do c

right and I'm taking only one pointer

like void estri

VP right and I'm taking in a is equal to

5 and one more thing that is float

suppose I'm taking float B is equal to

1.56 and

care care C at H is equal to uh anything

you can take like I'm taking

C right and now I'll access all the

three variables using one pointer only

so I'm first of all I'm writing VP is

equal to address of a and now I want to

dreference

this a is equal to

we are printing value of a and see if

you der reference like this s will be

simple so it will give you error let me

run

this here we it is giving error like d

referencing word pointer and invalid use

of word expression so we cannot this

deference this word pointer something

like this now we have to type cast it so

I'm typ casting it into integer pointer

first

and see now let me run this and it will

print a is equal to

5

see see it is printing the value a is

equal to 5 right now I want to access

that variable float so in VP I'm storing

address of B now so now this word

pointer is

pointing

what float variable so now B value is

equal to percentage

F and here I'm D referencing this now so

we have to convert it into

float we have to type cast it into float

see let me run this and it will give you

a equal to uh sorry this a is equal 5 b

is equal to 1.5

6 right and now same address of

CH and let me print

C = to percentage

C and uh

estri we now we have to type cast into

care

right and now let me print this sorry

run this see it is printing a b c uh CH

value all the three values so we are

accessing all the three data types

variables with a single pointer

only so that is benefit of using word

pointer that is why programmers use this

word pointer right