What is nullptr and how to use it in C++

In C++11 and later versions, nullptr is a special literal that represents a null pointer (i.e., a pointer that does not point to a valid address)

Before C++11, we had to use NULL or 0. But this led to ambiguity errors, especially when working with overloaded functions and templates.

Additionally, it improves readability and helps prevent difficult-to-detect errors related to memory management.

Declaration of null pointers

To declare a null pointer in C++11 and later versions, we simply initialize it to nullptr. This ensures that the pointer does not have a valid address assigned.

#include <iostream>

int main() {
    int* ptr = nullptr; // Pointer to int initialized to nullptr

    if (ptr == nullptr) {
        std::cout << "The pointer does not point to any valid address." << std::endl;
    }

    return 0;
}

Advantages of nullptr

The main advantage of nullptr lies in its ability to enhance the safety and clarity of the code. For example, let’s imagine this scenario,

#include <iostream>

void func(int x) {
    std::cout << "func(int) called with " << x << std::endl;
}

void func(int* ptr) {
    if (ptr) {
        std::cout << "func(int*) called with valid pointer." << std::endl;
    } else {
        std::cout << "func(int*) called with null pointer." << std::endl;
    }
}

int main() {
    func(0);       // Ambiguous with NULL, interpreted as `func(int)`
    func(nullptr); // Clear: calls `func(int*)` with null pointer

    return 0;
}