[class.nest]

# 11 Classes [[class]](./#class)

## 11.4 Class members [[class.mem]](class.mem#class.nest)

### 11.4.12 Nested class declarations [class.nest]

[1](#1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/classes.tex#L3111)

A class can be declared within another class[.](#1.sentence-1)

A class declared within
another is called a [*nested class*](#def:class,nested "11.4.12 Nested class declarations [class.nest]")[.](#1.sentence-2)

[*Note [1](#note-1)*:

See [[expr.prim.id]](expr.prim.id "7.5.5 Names") for restrictions on the use of non-static data
members and non-static member functions[.](#1.sentence-3)

— *end note*]

[*Example [1](#example-1)*: int x;int y;

struct enclose {int x; static int s; struct inner {void f(int i) {int a = sizeof(x); // OK, operand of sizeof is an unevaluated operand x = i; // error: assign to enclose​::​x s = i; // OK, assign to enclose​::​s::x = i; // OK, assign to global x y = i; // OK, assign to global y}void g(enclose* p, int i) { p->x = i; // OK, assign to enclose​::​x}};};

inner* p = 0; // error: inner not found — *end example*]

[2](#2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/classes.tex#L3146)

[*Note [2](#note-2)*:

Nested classes can be defined
either in the enclosing class or in an enclosing namespace;
member functions and static data members of a nested class can be
defined either in the nested class or in an enclosing namespace scope[.](#2.sentence-1)

[*Example [2](#example-2)*: struct enclose {struct inner {static int x; void f(int i); };};

int enclose::inner::x = 1;

void enclose::inner::f(int i) { /* ... */ }class E {class I1; // forward declaration of nested classclass I2; class I1 { }; // definition of nested class};class E::I2 { }; // definition of nested class — *end example*]

— *end note*]

[3](#3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/classes.tex#L3175)

A friend function ([[class.friend]](class.friend "11.8.4 Friends")) defined
within a nested class has no special access rights to
members of an enclosing class[.](#3.sentence-1)