6 Basics [basic]

6.5 Name lookup [basic.lookup]

6.5.4 Qualified name lookup [basic.lookup.qual] Class members [class.qual]

If the nested-name-specifier of a qualified-id nominates a class, the name specified after the nested-name-specifier is looked up in the scope of the class ([class.member.lookup]), except for the cases listed below.
The name shall represent one or more members of that class or of one of its base classes ([class.derived]).
[Note 1:
A class member can be referred to using a qualified-id at any point in its potential scope ([basic.scope.class]).
— end note]
The exceptions to the name lookup rule above are the following:
In a lookup in which function names are not ignored29 and the nested-name-specifier nominates a class C: the name is instead considered to name the constructor of class C.
[Note 2:
For example, the constructor is not an acceptable lookup result in an elaborated-type-specifier so the constructor would not be used in place of the injected-class-name.
— end note]
Such a constructor name shall be used only in the declarator-id of a declaration that names a constructor or in a using-declaration.
[Example 1: struct A { A(); }; struct B: public A { B(); }; A::A() { } B::B() { } B::A ba; // object of type A A::A a; // error: A​::​A is not a type name struct A::A a2; // object of type A — end example]
A class member name hidden by a name in a nested declarative region or by the name of a derived class member can still be found if qualified by the name of its class followed by the ​::​ operator.
Lookups in which function names are ignored include names appearing in a nested-name-specifier, an elaborated-type-specifier, or a base-specifier.