Is it safe to delete a NULL pointer?

Deleting a nullptr pointer in C++ is safe. According to the C++ standard, when the delete operator receives a nullptr pointer, it does nothing. This means that attempting to delete a pointer that is already nullptr will not cause the program to crash or produce runtime errors.

Why is this safe?

The C++ standard explicitly states that delete nullptr; has no effect. This is a defensive programming practice that prevents multiple deletions of the same object. Without this rule, programmers would need to manually check if the pointer is nullptr before calling delete, which would make the code more complex and prone to errors.

Example

Consider the following code snippet:

cpp
int* ptr = new int(10);  // Allocate memory and initialize
delete ptr;             // Delete the memory it points to
ptr = nullptr;          // Set ptr to nullptr

// Calling delete here is safe because ptr is nullptr
delete ptr;

In this example, even if ptr has been set to nullptr, the second call to delete ptr; is completely safe, with no runtime errors or undefined behavior.

Summary

Overall, although deleting a nullptr pointer is safe, the best practice is to set the pointer to nullptr after deletion to avoid dangling pointer issues. This ensures that even if the pointer is deleted again, the program will not exhibit abnormal behavior.