Why Does Calling a Class Method with a Null Pointer Sometimes Work in C ?

Accessing Class Methods via Invalid Class Pointers

Some programming scenarios involve accessing class methods through null class pointers. Consider the following example:

class ABC {
public:
    int a;
    void print() { cout << "hello" << endl; }
};

int main() {
    ABC* ptr = NULL;
    ptr->print();
    return 0;
}

surprisingly, this code manages to run without any errors. How is this possible?

Undefined Behavior

In C , calling member functions using a pointer that doesn't reference a valid object constitutes undefined behavior. This means that the behavior of the program is unpredictable and can vary widely.

Exception in this Case

In the provided code, the member function print() happens to not utilize the this pointer, which serves as a reference to the object. This peculiar situation allows the code to run seemingly without issue.

However, it's crucial to recognize that relying on such undefined behavior is dangerous and can lead to unexpected problems in different scenarios.

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