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# this pointer

From cppreference.com
< cpp‎ | language

### [edit] Syntax

`this` |  |

The keyword `this` is a prvalue expression whose value is the address of the object, on which the member function is being called. It can appear in the following contexts:

1) Within the body of any non-static member function, including member initializer list
2) within the declaration of a non-static member function anywhere after the (optional) cv-qualifier sequence, including dynamic exception specification(deprecated), noexcept specification(C++11), and the trailing return type(since C++11)
3) within default member initializer (since C++11)

The type of `this` in a member function of class `X` is `X*` (pointer to X). If the member function is cv-qualified, the type of `this` is `cv X*` (pointer to identically cv-qualified X). Since constructors and destructors cannot be cv-qualified, the type of `this` in them is always `X*`, even when constructing or destroying a const object.

When a non-static class member is used in any of the contexts where the `this` keyword is allowed (non-static member function bodies, member initializer lists, default member initializers), the implicit `this->` is automatically added before the name, resulting in a member access expression (which, if the member is a virtual member function, results in a virtual function call).

In class templates, `this` is a dependent expression, and explicit `this->` may be used to force another expression to become dependent.

During construction of an object, if the value of the object or any of its subobjects is accessed through a glvalue that is not obtained, directly or indirectly, from the constructor's `this` pointer, the value of the object or subobject thus obtained is unspecified. In other words, the this pointer cannot be aliased in a constructor:

    extern struct D d;
    struct D {
        D(int a) : a(a), b(d.a) {} // b(a) or b(this->a) would be correct
        int a, b;
    };
    D d = D(1);   // because b(d.a) did not obtain a through this, d.b is now unspecified

It is possible to execute delete this;, if the program can guarantee that the object was allocated by new, however, this renders every pointer to the deallocated object invalid, including the `this` pointer itself: after delete this; returns, such member function cannot refer to a member of a class (since this involves an implicit dereference of `this`) and no other member function may be called. This is used, for example, in the member function of the control block of std::shared_ptr responsible for decrementing the reference count, when the last reference to the managed object goes out of scope.

    class ref
    {
        // ...
        void incRef() { ++mnRef; }
        void decRef() { if (--mnRef == 0) delete this; }
    };

### [edit] Example

    class T
    {
        int x;

        void foo()
        {
            x = 6;       // same as this->x = 6;
            this->x = 5; // explicit use of this->
        }

        void foo() const
        {
    //        x = 7; // Error: *this is constant
        }

        void foo(int x) // parameter x shadows the member with the same name
        {
            this->x = x; // unqualified x refers to the parameter
                         // 'this->' required for disambiguation
        }

        int y;
        T(int x) : x(x), // uses parameter x to initialize member x
                   y(this->x) // uses member x to initialize member y
        {}

        T& operator= ( const T& b )
        {
            x = b.x;
            return *this; // many overloaded operators return *this
        }
    };

    class Outer {
        int a[sizeof(*this)]; // error: not inside a member function
        unsigned int sz = sizeof(*this); // OK: in default member initializer
        void f() {
            int b[sizeof(*this)]; // OK
            struct Inner {
                int c[sizeof(*this)]; // error: not inside a member function of Inner
            };
        }
    }

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