Before the introduction of nullptr, the NULL macro or plain 0 was commonly used to represent a null pointer. However, using nullptr is preferred because it has a distinct type, std::nullptr_t, and can be used in contexts where the old-style NULL or 0 might lead to ambiguities or errors.

Here’s an example of using nullptr in C++:

int* ptr = nullptr;  // initializing a pointer with nullptr

In this example, ptr is assigned a null pointer using nullptr.

Using nullptr instead of NULL or 0 can improve code readability and help catch certain types of errors, making it a recommended practice in modern C++ programming.

Reference:

• Stroustrup, Bjarne. (2013). The C++ Programming Language, Fourth Edition. Addison-Wesley Professional.