C++ CoreLesson 38 of 441 min read7 questions

The this Keyword

A pointer to the current object, available inside non-static member functions.

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Concept core idea Watch out easy to get wrong

Concept

Key concepts

this is a pointer available in every non-static member function, holding the address of the object the function was called on.
Type: non-const method -> Entity* const (can change the object, can't reseat the pointer); const method -> const Entity* const (can't change the object either).
this = the pointer (address); *this = the object. Use this->m or (*this).m; return *this by reference (Entity&) for chaining — returning it by value copies.
Main uses: disambiguate a member from a same-named parameter (this->a = a;), return *this for chaining, and self-comparison (this == &other).
this-> is optional for member access — needed only to disambiguate a same-named parameter (or dependent names in templates).
Static member functions have no this (not tied to an object). The compiler passes this as a hidden first argument to each non-static call.

The three main uses of this

C++

class Entity {
    int a;
public:
    Entity(int a) { this->a = a; }              // (a) disambiguate member vs parameter

    Entity& setA(int a) { this->a = a; return *this; }   // (b) chain: e.setA(1).setA(2);

    Entity& operator=(const Entity& rhs) {
        if (this == &rhs) return *this;         // (c) self-assignment guard
        a = rhs.a;
        return *this;
    }

    int getA() const { return a; }              // const member: this is const Entity* const
};

Watch out

Easily confused

this vs *this

this = the pointer (address of the object). *this = the object itself. Return *this by reference to chain.

non-const vs const member this

non-const method: Entity* const (can change the object). const method: const Entity* const (can't change it).

this-> optional vs required

Member access usually needs no this->. Required only to disambiguate a same-named parameter (or dependent names in templates).

Test yourself

7 questions on this lesson. Write your answers from memory, then compare them with the model answers side by side.

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