The injected-class-name is the unqualified name of a class within the scope of said class.

In aclass template, the injected-class-name can be used either as a template name that refers to the current template, or as a class name that refers to the current instantiation.

[edit]Explanation

In aclass scope, the class name of the current class or the template name of the current class template is treated as if it were a public member name; this is calledinjected-class-name. The point of declaration of the name is immediately following the opening brace of the class (template) definition.

int X; struct X{void f(){        X* p;// OK, X is an injected-class-name::X* q;// Error: name lookup finds a variable name, which hides the struct name}}; template<class T>struct Y{void g(){        Y* p;// OK, Y is an injected-class-name        Y<T>* q;// OK, Y is an injected-class-name, but Y<T> is not}};

Like other members, injected-class-names are inherited. In the presence of private or protected inheritance, the injected-class-name of an indirect base class might end up being inaccessible in a derived class.

struct A{};struct B:private A{};struct C:public B{    A* p;// Error: injected-class-name A is inaccessible::A* q;// OK, does not use the injected-class-name};

[edit]In class template

The injected-class-name of a class template can be used as a template-name or a type-name.

In the following cases, the injected-class-name is treated as a template-name of the class template itself:

• It is followed by<.
• It is used as atemplate template argument.
• It is the final identifier in theelaborated class specifier of a friend class template declaration.

Otherwise, it is treated as a type-name, and is equivalent to the template-name followed by the template-parameters of the class template enclosed in<>.

template<template<class,class>class>struct A; template<class T1,class T2>struct X{    X<T1, T2>* p;// OK, X is treated as a template-name using a= A<X>;// OK, X is treated as a template-name template<class U1,class U2>friendclass X;// OK, X is treated as a template-name     X* q;// OK, X is treated as a type-name, equivalent to X<T1, T2>};

Within the scope of a classtemplate specialization orpartial specialization, when the injected-class-name is used as a type-name, it is equivalent to the template-name followed by the template-arguments of the class template specialization or partial specialization enclosed in<>.

template<>struct X<void,void>{    X* p;// OK, X is treated as a type-name, equivalent to X<void, void> template<class,class>friendclass X;// OK, X is treated as a template-name (same as in primary template)     X<void,void>* q;// OK, X is treated as a template-name}; template<class T>struct X<char, T>{    X* p, q;// OK, X is treated as a type-name, equivalent to X<char, T> using r= X<int,int>;// OK, can be used to name another specialization};

The injected-class-name of a class template or class template specialization can be used either as a template-name or a type-name wherever it is in scope.

template<>class X<int,char>{class B{        X a;// meaning X<int, char> template<class,class>friendclass X;// meaning ::X};}; template<class T>struct Base{    Base* p;// OK: Base means Base<T>}; template<class T>struct Derived:public Base<T*>{typename Derived::Base* p;// OK: Derived::Base means Derived<T>::Base,// which is Base<T*>}; template<class T,template<class>class U= T::template Base>struct Third{}; Third<Derived<int>> t;// OK: default argument uses injected-class-name as a template

A lookup that finds an injected-class-name can result in an ambiguity in certain cases (for example, if it is found in more than one base class). If all of the injected-class-names that are found refer to specializations of the same class template, and if the name is used as a template-name, the reference refers to the class template itself and not a specialization thereof, and is not ambiguous.

template<class T>struct Base{}; template<class T>struct Derived: Base<int>, Base<char>{typename Derived::Base b;// error: ambiguoustypename Derived::Base<double> d;// OK};

[edit]injected-class-name and constructors

Constructors do not have names, but the injected-class-name of the enclosing class is considered to name a constructor in constructor declarations and definitions.

In a qualified nameC::D, if

• name lookup does not ignore function names, and
• lookup ofD in the scope of the classC finds its injected-class-name

the qualified name is always considered to nameC's constructor. Such a name can only be used in the declaration of a constructor (e.g. in a friend constructor declaration, a constructor template specialization, constructor template instantiation, or constructor definition) or be used to inherit constructors(since C++11).

struct A{    A();    A(int); template<class T>    A(T){}};using A_alias= A; A::A(){}A_alias::A(int){}template A::A(double); struct B: A{using A_alias::A;}; A::A a;// Error: A::A is considered to name a constructor, not a typestruct A::A a2;// OK, same as 'A a2;'B::A b;// OK, same as 'A b;'

[edit]Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

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