Types of Pointers in C

Pointers in C can be classified into many different types based on the parameter on which we are defining their types. If we consider the type of variable stored in the memory location pointed by the pointer, then the pointers can be classified into the following types:

1. Integer Pointers

As the name suggests, these are the pointers that point to the integer values.

Syntax

int *ptr;

These pointers are pronounced as Pointer to Integer.

Similarly, a pointer can point to any primitive data type. It can point also point to derived data types such as arrays and user-defined data types such as structures.

2. Array Pointer

Pointers and Array are closely related to each other. Even the array name is the pointer to its first element. They are also known as Pointer to Arrays. We can create a pointer to an array using the given syntax.

Syntax

char *ptr = &array_name;

Pointer to Arrays exhibits some interesting properties which we discussed later in this article.

3. Structure Pointer

The pointer pointing to the structure type is called Structure Pointer or Pointer to Structure. It can be declared in the same way as we declare the other primitive data types.

Syntax

struct struct_name *ptr;

In C, structure pointers are used in data structures such as linked lists, trees, etc.

4. Function Pointers

Function pointers point to the functions. They are different from the rest of the pointers in the sense that instead of pointing to the data, they point to the code. Let’s consider a function prototype – int func (int, char), the function pointer for this function will be

Syntax

int (*ptr)(int, char);

Note: The syntax of the function pointers changes according to the function prototype.

5. Double Pointers

In C language, we can define a pointer that stores the memory address of another pointer. Such pointers are called double-pointers or pointers-to-pointer. Instead of pointing to a data value, they point to another pointer.

Syntax

datatype ** pointer_name;

Dereferencing Double Pointer

*pointer_name; // get the address stored in the inner level pointer
**pointer_name; // get the value pointed by inner level pointer

Note: In C, we can create multi-level pointers with any number of levels such as – ***ptr3, ****ptr4, ******ptr5 and so on.

6. NULL Pointer

The Null Pointers are those pointers that do not point to any memory location. They can be created by assigning a NULL value to the pointer. A pointer of any type can be assigned the NULL value.

Syntax

data_type *pointer_name = NULL;
        or
pointer_name = NULL

It is said to be good practice to assign NULL to the pointers currently not in use.

7. Void Pointer

The Void pointers in C are the pointers of type void. It means that they do not have any associated data type. They are also called generic pointers as they can point to any type and can be typecasted to any type.

Syntax

void * pointer_name;

One of the main properties of void pointers is that they cannot be dereferenced.

8. Wild Pointers

The Wild Pointers are pointers that have not been initialized with something yet. These types of C-pointers can cause problems in our programs and can eventually cause them to crash. If values is updated using wild pointers, they could cause data abort or data corruption.

Example

int *ptr;
char *str;

9. Constant Pointers

In constant pointers, the memory address stored inside the pointer is constant and cannot be modified once it is defined. It will always point to the same memory address.

Syntax

data_type * const pointer_name;

10. Pointer to Constant

The pointers pointing to a constant value that cannot be modified are called pointers to a constant. Here we can only access the data pointed by the pointer, but cannot modify it. Although, we can change the address stored in the pointer to constant.

Syntax

const data_type * pointer_name;

Other Types of Pointers in C:

There are also the following types of pointers available to use in C apart from those specified above:

• Far pointer: A far pointer is typically 32-bit that can access memory outside the current segment.
• Dangling pointer: A pointer pointing to a memory location that has been deleted (or freed) is called a dangling pointer.
• Huge pointer: A huge pointer is 32-bit long containing segment address and offset address.
• Complex pointer: Pointers with multiple levels of indirection.
• Near pointer: Near pointer is used to store 16-bit addresses means within the current segment on a 16-bit machine.
• Normalized pointer: It is a 32-bit pointer, which has as much of its value in the segment register as possible.
• File Pointer: The pointer to a FILE data type is called a stream pointer or a file pointer.

Pointers are one of the core components of the C programming language. A pointer can be used to store the memory address of other variables, functions, or even other pointers. The use of pointers allows low-level memory access, dynamic memory allocation, and many other functionality in C.

In this article, we will discuss C pointers in detail, their types, uses, advantages, and disadvantages with examples.