When should I make explicit use of the `this` pointer?

Usually, you do not have to, this-> is implied.

Sometimes, there is a name ambiguity, where it can be used to disambiguate class members and local variables. However, here is a completely different case where this-> is explicitly required.

Consider the following code:

template<class T>
struct A {
   T i;
};

template<class T>
struct B : A<T> {
    T foo() {
        return this->i; //standard accepted by all compilers 
        //return i; //clang and gcc will fail
        //clang 13.1.6: use of undeclared identifier 'i'
        //gcc 11.3.0: 'i' was not declared in this scope
        //Microsoft C++ Compiler 2019 will accept it
    }

};

int main() {
    B<int> b;
    b.foo();
}

If you omit this->, some compilers do not know how to treat i. In order to tell it that i is indeed a member of A<T>, for any T, the this-> prefix is required.

Note: it is possible to still omit this-> prefix by using:

template<class T>
struct B : A<T> {
    int foo() {
        return A<T>::i; // explicitly refer to a variable in the base class 
        //where 'i' is now known to exist
    }

};

If you declare a local variable in a method with the same name as an existing member, you will have to use this->var to access the class member instead of the local variable.

#include <iostream>
using namespace std;
class A
{
    public:
        int a;

        void f() {
            a = 4;
            int a = 5;
            cout << a << endl;
            cout << this->a << endl;
        }
};

int main()
{
    A a;
    a.f();
}

prints:

5
4

There are several reasons why you might need to use this pointer explicitly.

• When you want to pass a reference to your object to some function.
• When there is a locally declared object with the same name as the member object.
• When you're trying to access members of dependent base classes.
• Some people prefer the notation to visually disambiguate member accesses in their code.