8 Expressions [expr]

The keyword this names a pointer to the object for which a non-static member function is invoked or a non-static data member's initializer ([class.mem]) is evaluated.

If a declaration declares a member function or member function template of a class X, the expression this is a prvalue of type “pointer to cv-qualifier-seq X” between the optional cv-qualifier-seq and the end of the function-definition, member-declarator, or declarator. It shall not appear before the optional cv-qualifier-seq and it shall not appear within the declaration of a static member function (although its type and value category are defined within a static member function as they are within a non-static member function). [ Note: This is because declaration matching does not occur until the complete declarator is known.  — end note ] Unlike the object expression in other contexts, *this is not required to be of complete type for purposes of class member access outside the member function body. [ Note: Only class members declared prior to the declaration are visible.  — end note ] [ Example:

struct A {
  char g();
  template<class T> auto f(T t) -> decltype(t + g())
    { return t + g(); }
};
template auto A::f(int t) -> decltype(t + g());

 — end example ]

Otherwise, if a member-declarator declares a non-static data member of a class X, the expression this is a prvalue of type “pointer to X” within the optional default member initializer. It shall not appear elsewhere in the member-declarator.

The expression this shall not appear in any other context. [ Example:

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
    };
  }
};

 — end example ]