Why Do I Have to Access Template Base Class Members Through the 'this' Pointer?

In C++, when we have a class template that inherits from a template base class, we need to explicitly use this pointer to access members of the base class. In this article, we will learn why it is necessary to access template base class members through 'this' pointer in C++.

The Problem in Accessing Template Base Class Members Without this Pointer

When a template class derives from another template class, the base class's members are considered dependent on the template parameters and are unknown to the compiler until the template is instantiated. This creates a problem where the derived class template does not automatically consider the base class scope when compiling the template. As a result, if we try to use a base class member directly in the derived class without qualification, the compiler can't do anything meaningful to fix it in the first stage of compilation.

In the following program, we try to access the template base class members without this pointer to see what are the consequences:

Output

error: there are no arguments to 'display' that depend on a template parameter, so a declaration of 'display' 
must be available [-fpermissive]

Using 'this' Pointer to Access Template Base Class Members

To resolve the issue of dependent names, we can use the in the derived class to make sure that the name should be looked up in the context of the base class only. The this pointer is a pointer to the current instance of the class, so using it we can guide the compiler about where to look for the name.

C++ Program to Access Template Base Class Members through 'this' Pointer

The below example demonstrates the use of the ‘this’ pointer to access base class members in a class template.

Hello Geeks

Time Complexity: O(1)
Auxiliary Space: O(1)