Is Checking \'this\' for Null Ever Necessary in C ?

On the Usefulness of Checking "this" for Null

In programming, the "this" pointer refers to the current object instance within a member function. It allows the function to access the object's data and methods. However, a question arises: Does it ever make sense to check if "this" is null?

Let's consider a method that performs a task within a class:

<code class="cpp">class MyClass {
public:
    int myFunction() {
        if (this == nullptr) {
            return -1; // Error code
        }
        ...
    }
};
</code>

The question is whether this null check is necessary or even valid.

According to the C standard, any call on a null pointer is undefined behavior. This means that if the "this" pointer is null, the method call is invalid and the behavior of the program is unpredictable. Therefore, in standard C , checking if "this" is null is not sensible.

However, some implementations allow the use of "this == 0" for non-virtual functions. As a result, libraries written specifically for these implementations may rely on this hack.

In certain cases, the null check can be added as a debugging aid to catch instances where the "this" pointer is unexpectedly null due to a caller's mistake. However, the preferred method for debugging such issues is to use asserts.

Additionally, it's important to note that checking if "this" is null does not necessarily mean that the object is deleted. It only signifies that a method call was made on a null pointer or reference obtained from a null pointer, which is inherently incorrect behavior in C .

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