17 Jul C – Pointers

The C Pointer is a variable that is used to store the memory address as its value. However, to get the memory address of a variable, use the & operator. This means a variable has a unique memory location. This memory location has its address. To access this address, we use the ampersand, i.e., the & operator.

Before moving further, we’ve prepared a video tutorial to understand what Pointers are in C:

Video: Pointers in C

Video: Pointers in C (Hindi)

In this lesson, we will discuss the two operators useful to understand the concept of Pointers in C:

• The Address Operator: Access the address of a variable. Defined by &, the ampersand sign.
• The Indirection Operator: Access the value of an address. Defined by *, the asterisk sign.

Advantages of Pointers

• Efficiency: Direct access to memory and hardware improves performance.
• Dynamic Memory: They enable the dynamic allocation and deallocation of memory, avoiding wastage.
• Complex Data Structures: Pointers are fundamental for creating complex data structures like linked lists and trees.
• Function Pointers: These allow for callback functions and better modularity in code.

Disadvantages of Pointers

• Complexity: They can make the code more complex and harder to understand.
• Debugging Issues: Pointer-related bugs like segmentation faults and memory leaks are hard to debug.
• Security Risks: Incorrect usage can lead to vulnerabilities like buffer overflow.
• Memory Management: Manual memory management can be prone to errors, such as not freeing up memory, leading to memory leaks.

Let us see an example to display the address of variables in C:

#include <stdio.h>

int main()
{
   int a;
   float b;
   char c;

   printf("Address of variable a = %p",&a);
   printf("\nAddress of variable b = %p",&b);
   printf("\nAddress of variable c = %p",&c);

   return 0;
}

Output

Address of variable a = 0x7fffb239b8a0
Address of variable b = 0x7fffb239b8a4
Address of variable c = 0x7fffb239b89f

Syntax

dataType *varName;

Above, varName is the pointer variable, whereas datatype is the type.

Declare and create a Pointer

Follow the above syntax and let us see how we can create and declare pointers:

int* a;

In C, both int *a; and int* a; are syntactically correct and do the same thing: they declare a pointer to an integer.

Example

Let us now see an example is to create a pointer variable and point to an integer variable. Here, The int* b declares b as a pointer to an integer:

The int*b = &a means that b is a pointer to an integer, and it is being initialized with the address of a.

#include <stdio.h>

int main()
{
   // Integer variable a
   int a = 10;
   
   // A pointer variable b storing the address of the variable a
   int* b = &a; 

   printf("Integer Value = %d",a);
   printf("\nAddress of a (using &a) %p",&a);
   printf("\nAddress of a (using pointer b) = %p",b);

   return 0;
}

Output

Integer Value = 10
Address of a (using &a) 0x7ffcfc4e1d34
Address of a (using pointer b) = 0x7ffcfc4e1d34