Void Pointer in C

Last Updated on January 8, 2024 by Ankit Kochar

In the realm of C programming, void pointers stand as a unique construct, offering both flexibility and complexity. Unlike pointers of other types, void pointers lack a specific data type association, allowing them to point to data of any type. This versatility makes them a powerful tool in certain programming scenarios, yet their usage requires a nuanced understanding due to the absence of a fixed data type. This article aims to delve into the concept of void pointers in C, exploring their definition, usage, advantages, and potential pitfalls.

What is a Void Pointer in C?

The Void Pointer in C is defined as the type of pointer which does not have any associated data type. It can point to any data type like integer, character, structure, and also to other pointers. The usage of the void pointer in C allows a greater deal of flexibility in programming as it allows the functions and data structure in C to be defined to work with any data type. This is why it is also known as a Generic Pointer.

Syntax of the Void Pointer in C

The void Pointer in C is declared using a special keyword “void”, which indicates that it can be used with any data type. Here is the syntax for declaring a void pointer in C Language.

void *ptrName;

This statement declares a void pointer in C named, “ptrName”. Being a void pointer, it can point to any data type.

Working of Void Pointer in C

The void pointer in C works by storing the address of a memory location. As mentioned above, since it has no data type associated with it, it doesn’t know about the data that it is pointing to. So, the void pointer in C cannot be used to directly access the value of the data that it is pointing to.

To use a void pointer in C, it must be cast to a specific data type in C. This typecasting helps the compiler to determine the size and structure of the data that it is pointing to. This allows the void pointer in C to be dereferenced and used.

Let us see an example to learn it in a better way. This example shows how to use a void pointer in C to allocate memory for an integer.

void *ptr;
int *iptr;
ptr = malloc(sizeof(int));
iptr = (int*)ptr;

• In the above code snippet, we have declared
  • a void pointer named, “ptr”
  • an integer pointer “iptr”.
• Then we allocated the memory using the malloc() Function and then assigned the address of this memory to the integer pointer named, “iptr”.
• Then we have typecast the void pointer “ptr” to an integer pointer using the line “iptr = (int*) ptr”.
• This statement allows the “ptr” to be used to access the value of the integer stored in the allocated memory.

Size of Void Pointer in C

The size of the Void Pointer in C depends on the type of Platform you are using. For 32-Bit Architecture: 4 Bytes
For 64-Bit Architecture: 8 Bytes

Here is the code which is checking the size of void pointer in C.

#include <stdio.h> 

int main()  
{  
    void *ptr;		//void pointer  
    int *iptr;		// integer pointer  
    char *cptr;		//character pointer  
    float *fptr;	//float pointer  
    
    //size of void pointer  
    printf("size of void pointer = %d\n",sizeof(ptr)); 
    
    //size of integer pointer  
    printf("size of integer pointer = %d\n",sizeof(iptr)); 
    
    //size of character pointer  
    printf("size of character pointer = %d\n",sizeof(cptr)); 
    
    //size of float pointer  
    printf("size of float pointer = %d\n",sizeof(fptr));  
    
    return 0;  
}

Output

size of void pointer = 8
size of integer pointer = 8
size of character pointer = 8
size of float pointer = 8

Here, we have printed the size of the void pointer, which comes out to be 8 bytes as we are using a 64-bit computer. Also, we have printed the size of the other types of pointers to demonstrate that size of each type of pointer is almost the same as all of them are storing the addresses of memory.

Examples of Void Pointer in C

These examples will help in clear understanding of the topic i.e., Void Pointer in C.

Example 1 of Void Pointer in C
This example shows that void pointer in C can store objects of any type and we can access the object of any type with the help of the proper typecasting.

Code

#include<stdio.h>   

int main()   
{   
    int a = 56; 
    float b = 4.5; 
    char c = 'k';   
    
    void *ptr; // declaration of void pointer.  
   
    // assigning the address of variable 'a'.  
    ptr=&a;  
    printf("value of 'a' is : %d",*((int*)ptr));  
   
    // assigning the address of variable 'b'.  
    ptr=&b;  
    printf("\nvalue of 'b' is : %f",*((float*)ptr));  
    
    // assigning the address of variable 'c'.  
    ptr=&c;  
    printf("\nvalue of 'c' is : %c",*((char*)ptr));  
    return 0;  
}

Output

value of 'a' is : 56
value of 'b' is : 4.500000
value of 'c' is : k

Explanation
In this example, we have declared a void pointer to access the value of different types of variables. First, it is used to access an integer by typecasting it into an int pointer. Similarly, it is used for accessing the double and character values.

Example 2 of Void Pointer in C
This example will demonstrate to you that the void pointer in C can be used to implement generic functions in C.

Code

#include <stdio.h>

void swap(void *ptr1, void *ptr2, size_t size) {
    void *temp = malloc(size);
    memcpy(temp, ptr1, size);
    memcpy(ptr1, ptr2, size);
    memcpy(ptr2, temp, size);
    free(temp);
}

int main() {
    int x = 5, y = 10;
    double a = 1.5, b = 2.5;
    char c1 = 'a', c2 = 'b';
    
    printf("Before swap: x = %d, y = %d\n", x, y);
    swap(&x, &y, sizeof(int));
    printf("After swap: x = %d, y = %d\n", x, y);
    
    printf("Before swap: a = %lf, b = %lf\n", a, b);
    swap(&a, &b, sizeof(double));
    printf("After swap: a = %lf, b = %lf\n", a, b);
    
    printf("Before swap: c1 = %c, c2 = %c\n", c1, c2);
    swap(&c1, &c2, sizeof(char));
    printf("After swap: c1 = %c, c2 = %c\n", c1, c2);
    
    return 0;
}

Output

Before swap: x = 5, y = 10
After swap: x = 10, y = 5
Before swap: a = 1.500000, b = 2.500000
After swap: a = 2.500000, b = 1.500000
Before swap: c1 = a, c2 = b
After swap: c1 = b, c2 = a

Explanation
In the above example, the swap() function is implemented using a void pointer. The function accepts two void pointers, ‘ptr1’ and ‘ptr2’, and a size_t variable ‘size’ that specifies the size of the data being swapped. The function allocates memory for a temporary variable ‘temp’, and uses the memcpy() function to copy the data pointed to by ‘ptr1’ to ‘temp’. The function then copies the data pointed to by ‘ptr2’ to ‘ptr1’, and the data pointed to by ‘temp’ to ‘ptr2’. Finally, the function frees the memory allocated for ‘temp’.

In the main() function, the swap() function is called three times, each with different data types. The function works correctly with all three data types and we got the expected output on the console.

Uses of Void Pointer in C

Some common uses of the Void Pointer in C are listed below as.

• Void Pointer in C is used for implementing the generic function. These functions take a void pointer as an argument and typecast them as per the requirement.
• Generic Data Structures are implemented using the Void Pointer in C because they can be typecast according to the data type.
• Void Pointer in C is used for Dynamic Memory Allocation as functions such as calloc and malloc return a void pointer which can be typecast into different types of pointers.

Limitations of Void Pointer in C

The Void Pointer in C faces the following limitations.

• The Void Pointer in C cannot be dereferenced directly. It must be typecast into other types to access values stored at the memory location.
• We cannot perform Pointer arithmetic operations on void Pointer in C. To perform operations, they need to be converted into an appropriate Data type.

Conclusion
In conclusion, we can say that the void pointer in C is a powerful tool that helps the programmer in dealing with various data types. The Void Pointer in C is not associated with any data type and can be cast into any other data type as per the requirement. Void Pointer in C helps in implementing the generic functions, generic data structure, and dynamic memory allocation.

Frequently Asked Questions (FAQs) Based on void Pointer in C

Some Frequently Asked Questions related to “Void Pointer in C” are given below.

1. How is a void pointer different from other pointers in C?
Unlike other pointers in C, void pointers (void *) do not have a fixed data type. They can be used to store the address of any type of data.

2. How do you dereference a void pointer?
Dereferencing a void pointer requires explicit casting to the appropriate data type. For example, if a void pointer points to an integer, it must be cast to an integer pointer before dereferencing.

3. What are the common use cases for void pointers in C?
Void pointers are often used in scenarios where the data type is not known at compile time, such as in generic functions or data structures that need to handle different types of data.

4. Can void pointers be used for arithmetic operations?
No, void pointers cannot directly participate in arithmetic operations as they lack a specific size due to their undefined data type.

5. How can memory be allocated for a void pointer?
Memory for a void pointer can be allocated using functions like malloc or calloc. The pointer returned by these functions can then be assigned to a void pointer.

6. What precautions should be taken when using void pointers?
Proper type casting and ensuring that the void pointer points to the correct data type are crucial. Improper casting or incorrect data type handling can lead to runtime errors or undefined behavior.

7. Are void pointers type-safe in C?
No, void pointers bypass the type-checking mechanisms of the compiler, so the programmer must ensure type safety by correctly casting them to the appropriate data type.

8. Can void pointers be used interchangeably with other pointer types?
While void pointers can be used to store the address of any data type, they need to be cast explicitly to other pointer types before dereferencing or performing operations specific to that data type.