How to compare pointers in C/C++?

The pointers can be directly compared using relational operators. In this article, we will learn about the comparisons of the pointers with the help of examples.

Pointers Comparison in C and C++

In C/C++, we can directly compare the pointers using relational operators (==, !=, <, >, <=, >=). These operators are used to compare two variables, values, or pointers. It returns a Boolean true value when the comparison is correct otherwise, it is false.

The core syntaxes of C and C++ pointers are similar such as declaration, dereferencing, and pointer arithmetic. All of these are identical in behavior and still use * and & in the same way.

Example of C Pointers Comparison

In this example, we declare two integer pointers say (*p1 and *p2), and then randomly allocate these pointer memory addresses of 200 and 300 respectively. Then, we check the conditions p1 > p2 using an if-statement where address 200 is greater than 300 which results in false and else part printed.

#include<stdio.h>

int main()
{
   int *p2;
   int *p1;

   p2 = (int *)300;
   p1 = (int *)200;
    
   if(p1 > p2) {
      printf("P1 is greater than p2");
   } else {
      printf("P2 is greater than p1");
   }
return 0;
}

The above code produces the following result:

P2 is greater than p1

Example of C++ Pointers Comparison

In this example, we declare three pointers say (*ptr1, *ptr2, and *ptr3) where ptr2 has different memory allocation. While taking a comparison of each pointer with others it returns the result in the form of a boolean value.

#include<iostream>
using namespace std;

int main() {
   int a = 10, b = 20;
   int *ptr1 = &a;
   int *ptr2 = &b;
   int *ptr3 = &a;

   cout << "ptr1 == ptr2: " << (ptr1 == ptr2 ? "true" : "false") << endl;
   cout << "ptr1 == ptr3: " << (ptr1 == ptr3 ? "true" : "false") << endl;
   cout << "ptr1 != ptr2: " << (ptr1 != ptr2 ? "true" : "false") << endl;

   if (ptr1 < ptr2)
       cout << "ptr1 points to a lower address than ptr2" << endl;
   else
       cout << "ptr1 does not point to a lower address than ptr2" << endl;

   return 0;
}

The above code produces the following result:

ptr1 == ptr2: false
ptr1 == ptr3: true
ptr1 != ptr2: true
ptr1 points to a lower address than ptr2