Is it safe to delete a void pointer?

Deleting a null pointer in C++ is safe. Per the C++ standard, delete p first checks if p is nullptr; if it is, delete performs no operation.

Why is this designed this way?

This design enhances safety and convenience. Developers may sometimes forget whether a pointer has been released, or in complex programs, pointers might already be set to nullptr. This rule is highly beneficial as it prevents program crashes caused by attempting to delete a pointer that is already nullptr.

Example

Suppose we have a simple class Cat, where we create a pointer to a Cat object and release it when no longer needed:

cpp
class Cat {
public:
    Cat() { cout << "Cat created." << endl; }
    ~Cat() { cout << "Cat destroyed." << endl; }
};

int main() {
    Cat* myCat = new Cat();  // Dynamic memory allocation
    delete myCat;            // Memory deallocation
    myCat = nullptr;         // Set pointer to nullptr

    // Double deletion test
    delete myCat;            // This is safe because myCat is nullptr
    return 0;
}

In this example, attempting to delete the myCat pointer a second time (which is now nullptr) is safe because the C++ standard library's delete operation first checks if the pointer is nullptr.

Important Notes

While deleting a null pointer is safe, it is good practice to set the pointer to nullptr immediately after deletion. This prevents dangling pointer issues, where the pointer still references deallocated memory. Setting it to nullptr ensures subsequent deletions are safe and helps identify uninitialized pointer usage during debugging.