Is Calling a Method Through a Null Pointer in C Defined Behavior?

Does Calling a Method Through a Null Pointer Work in C ?

Similar to the duplicate question, let's examine this C program:

<code class="cpp">#include <iostream>
using namespace std;

class test {
    int i;
public:
    test(): i(0) { cout << "ctor called" << endl; }
    void show() {
        cout << "show fun called" << endl;
    }
};

int main(int argc, char *argv[]) {
    test *ptr = NULL;
    ptr->show();
    return 0;
}</code>

Here, we call the show() method on a null pointer (ptr), which raises the question: Is this a valid operation?

The Answer

Calling a method through a null pointer is not standard C and is considered undefined behavior. However, some compilers might optimize this code to run efficiently by skipping the check for the null pointer.

The reason for this is that the method doesn't actually need the this pointer to execute its code. The compiler knows the type of the pointer, thus it can find the method and run its code without checking the pointer's value.

While this behavior might be convenient for performance reasons, it's essential to recognize that it's not a guaranteed behavior and varies across different compilers and systems. Relying on this optimization can lead to unexpected and erroneous behavior in production code.

Therefore, it's always best practice to check for null pointers before using them, ensuring the integrity and predictability of your code.

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