C++ Pointers

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Introduction

Pointers is basically a variable that stores the address of some other variable. They are very powerful as they can create data structures dynamically and also can be used simulate call-by-reference. Another main use of pointers is used literate over array elements. A pointer can be declared using the following syntax:

Syntax:

Datatype *variable_name

Example:

int *data1;
String *data2;

How pointers can be used

  • The very first step is to define a variable.
  • In order to assign the address of a variable to another variable, the (&) unary operator is used that returns the address of the variable whose address is to be assigned.
  • We can retrieve the value from the pointer variable using (*) unary operator.

Now let us consider the following program that illustrates the working of pointers:

Source Code

#include <iostream>
using namespace std;

int main() {
   
    // Declare a pointer
    int *pointer;
   
    // Initialize an integer
    // variable
    int myInteger = 10;
   
    // Assign the address
    // of "myInteger" to "pointer"
    pointer = &myInteger;
   
    // Display the address
    cout << "Address of pointer is " << pointer << '\n' ;
   
    // Display the value
    // pointed by "pointer"
    cout << "The value stored at the address pointed by pointer is " << *pointer << '\n' ;
   
    return 0;
}

Output:

Output Description:

As you can see in the output, the address and the corresponding value have been displayed to console.

Passing values as a pointer

We can pass values as a pointer. The values in the pointer value can be changed by first dereferencing the pointer variable and assigning new values to it.

Consider the following program illustrating the working of call by pointer method:

Source Code

    #include <iostream>
    using namespace std;
   
    // helper() function
    // to modify values
    void helper(int* a, int* b)
    {
        // Add 10 to 'a'
        // after dereferencing it
        (*a) = (*a) + 10;
   
        // Add 10 to 'b'
        // after dereferencing it
        (*b) = (*b) + 10;
    }
   
   
    int main() {
       
        // Initializing integer variables
        int value1 = 10, value2 = 20;
       
        // Initialize an integer
        // variable and assigning values
        int* myInteger1;
        myInteger1 = &value1;
        int* myInteger2;
        myInteger2 = &value2;
       
        // Calling helper function
        // to modify values
        helper(myInteger1, myInteger2);
       
        // Print integers
        cout << "Integers after modification,\n";
        cout << "myInteger1: " << (*myInteger1) << " , " << "myInteger2: " << (*myInteger2) << '\n';
        return 0;
    }

write your code here: Coding Playground

Output:

Output Description:

As you can see, the values of myInteger1 and myInteger2 have been modified to 20 and 30.

Array name as pointers

The array name possesses the address of the very first element of the array. It means that if we have an array as arr then using both arr and &arr[0] are the same thing.

Source Code

#include <iostream>
using namespace std;


int main() {
   
    // Create an array
    int arr[4]  = {20, 30, 40, 10};
   
    // Create a pointer variable
    int *ptr;
   
    // Assign the address of the first element to ptr
    ptr = arr;
   
    cout << "The address of first element is equal to " << ptr << '\n';
    cout << "The array elements are:\n";
    cout << ptr[0] << ' ' <<  ptr[1] << ' ' << ptr[2] << ' ' << ptr[3];
 
    return 0;
}

Output:

write your code here: Coding Playground

Advantage of pointers

  • Pointers are quite helper as they reduce the code size and improves the performance.
  • The allow us to construct trees or graph like data structure.
  • Multiple values can be returned using pointers.
  • Using pointers we can access memory location in computer’s memory.

Conclusion

In this article, we discussed about pointers. We mainly talked about passing pointers to function and manipulating array values using pointers. We believe that this article has helped to enhance your knowledge of pointers.