7 Expressions [expr]

7.5 Primary expressions [expr.prim]

7.5.2 This [expr.prim.this]

1
#
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.
2
#
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
 ]
[ Note
:
In a trailing-return-type, the class being defined is not required to be complete for purposes of class member access.
Class members declared later are not visible.
[ 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
 ]
— end note
 ]
3
#
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.
4
#
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
 ]