C Pointers

Pointers in C

A pointer is a variable, which contains the address of another variable, i.e., it’s a variable which has the address of another variable as its value. The utilization of pointers is to access the memory and also, to govern the address (manipulation of address).

A pointer is a derived datatype, which is constructed with the primitive data type. The size of the pointer variable is 2-byte for any data types. The pointer variable allows us to occupy the memory in runtime.

Pointer variable can access the value that is outside of the function body.

For e.g., If a is a variable of type int having value \0 stored at address 3000 and address of a is assigned to some other variable b, then b is a pointer variable pointing to memory address stored in it. In simple words, b is a pointer variable containing the address of a (i.e., 3000).

Types of Pointers in C

We have 8 different types of pointers in C. These are as follows:

• Void Pointer
• Null Pointer
• Dangling Pointer
• Wild Pointer
• Complex Pointer
• Huge Pointer
• Near Pointer
• Far Pointer

 

1) Void Pointer in C

A pointer is said to be void when a pointer has no associated data type with it. In other words, it can point to any data type and also, it can be typecasted to any type.

Since a void pointer does not have any standard type (data type) it is also referred to as a generic pointer sometimes.

A pointer can be declared as a void pointer by simply using the keyword void.

Example:

int main()
{
int num = 5;
void *ptr = #


printf(“%d”, *ptr);
return 0;
}

Declaration/ Syntax :

void  *ptr = NULL;

Why Void Pointer?

The malloc function returns a void pointer on successful allocation of memory because the malloc() is not aware of the location it is pointing to.

Declaration

(void* ) malloc(size_t size)

Here, size_t is defined in <stdlib.h> as unsigned int.

Note 1: The malloc function will simply allocate a block of memory as specified in the heap and if it is successful, it returns a pointer which points to the first byte of the allocated memory. In case of failure, NULL is returned.

Note 2: malloc returns a void pointer on successful memory allocation.

Note: There is no support of any kind of arithmetic operation in the concept of void pointers, i.e., it does not provide support for this problem statement. The void pointer will make the use of ‘*’ operator to serve the entire purpose.

Drawbacks of void pointer in C

The above case points out some of the limitations of void pointers. These can be pointed out as follows

•  Pointer arithmetic is not possible with void pointer due to its concrete size.
•  It can’t be used as dereferenced.

In order to solve the above problem, there is a requirement to typecast the pointer variable and it is used for dereferencing as well. The limitations of void pointers introduce the need to typecast the pointer variables.

2) Null pointer

Another type of pointer under this classification is Null pointer. It is a special type of pointer that does not point to any memory location. In other words, if we assign a NULL value to a pointer, then the pointer is considered as a Null pointer.

Note: In case of null pointer, it always contains 0 or NULL as its value.

Example:

#include<stdio.h>  //header file


int main()
{
int *ptr = NULL; // declaration of null pointer
return 0;
}

Use of Null pointer

1. It is used to initialize a pointer when that pointer is not assigned any memory address for that instance of time.
2. It is useful for handling errors when using in-built functions like malloc function.

3) Wild pointer

A Wild pointer is a type of pointer which is used to point to some arbitrary memory location, that’s why it is referred to as Uninitialized pointers. The wild pointer is uninitialized and due to this, they  are not very efficient. .

Example:

int main()
{
int *ptr;  //This is a wild pointer
*ptr = 5;
return 0;
}

Note: The inefficiency occurs because,

they may point to some unknown memory location. This can cause program crashes.

4) Dangling pointer

Pointer which points to some non-existing memory location.

Example:

int main()
{
int *ptr = (int *)malloc (sizeOf(int));  
…
…
…
free(ptr);  //memory is released


return 0;
}

In the above code, when the free() function is executed, the memory assigned to ptr is released but the pointer is still pointing to the deallocated memory and hence it is called a Dangling pointer.

6) Huge pointer

A huge pointer can access memory outside the current segment and is typically of size 32 bit.

A Huge pointer is not fixed and hence the part within which a huge pointer is located can be changed.

7) Near pointer

A Near pointer is a pointer that is utilized to bit-address up to 16 bits. The near pointer’s 16-bits address is accessible within a given section of that computer memory which is 16-bit enabled.

Example:

#include<stdio.h>  //including header files
int main()
{
   int n  = 07;
   int near* ptr_nr;
   ptr_nr= &n;
   printf(“%d”,sizeof ptr_nr);
   return 0;
}

8) Far pointer

It is a 32-bit pointer and is special pointer because it can access memory outside that current segment.

Example:

#include<stdio.h>
int main()
{
  int f= 55;
  int far *ptr_fr;
  ptr_fr=&f;
  print(“%d”, sizeof ptr_fr);
  return 0;
}

Conclusion

The utilization of pointers is to access the memory and also, to govern the address (manipulation of address).

Pointers in C might be difficult to understand for beginners, but it is an essential part of programming in C.