[class.access.general] (original) (raw)

11 Classes [class]

11.8 Member access control [class.access]

11.8.1 General [class.access.general]

A member of a class can be

• private, that is, it can be named only by members and friends of the class in which it is declared;
• protected, that is, it can be named only by members and friends of the class in which it is declared, by classes derived from that class, and by their friends (see [class.protected]); or
• public, that is, it can be named anywhere without access restriction.

[Note 1:

A constructor or destructor can be named by an expression ([basic.def.odr]) even though it has no name.

— _end note_]

A member of a class can also access all the members to which the class has access.

A local class of a member function may access the same members that the member function itself may access.96

Members of a class defined with the keywordclassare private by default.

Members of a class defined with the keywordsstruct or unionare public by default.

[Example 1: class X { int a; };struct S { int a; }; — _end example_]

Access control is applied uniformly to declarations and expressions.

When a using-declarator is named, access control is applied to it, not to the declarations that replace it.

For an overload set, access control is applied only to the function selected by overload resolution.

[Example 2: struct S { void f(int);private: void f(double);};void g(S* sp) { sp->f(2); } — _end example_]

[Note 3:

Because access control applies to the declarations named, if access control is applied to atypedef-name, only the accessibility of the typedef or alias declaration itself is considered.

The accessibility of the entity referred to by the typedef-name is not considered.

[Example 3: class A { class B { };public: typedef B BB;};void f() { A::BB x; A::B y; } — _end example_]

— _end note_]

[Note 4:

Access control does not prevent members from being found by name lookup or implicit conversions to base classes from being considered.

— _end note_]

The interpretation of a given construct is established without regard to access control.

If the interpretation established makes use of inaccessible members or base classes, the construct is ill-formed.

All access controls in [class.access] affect the ability to name a class member from the declaration of a particular entity, including parts of the declaration preceding the name of the entity being declared and, if the entity is a class, the definitions of members of the class appearing outside the class's member-specification.

[Note 5:

This access also applies to implicit references to constructors, conversion functions, and destructors.

— _end note_]

[Example 4: class A { typedef int I; I f() pre(A::x > 0);friend I g(I) post(A::x <= 0);static I x;template<int> struct Q;template<int> friend struct R;protected: struct B { };}; A::I A::f() pre(A::x > 0) { return 0; }A::I g(A::I p = A::x) post(A::x <= 0); A::I g(A::I p) { return 0; }A::I A::x = 0;template<A::I> struct A::Q { };template<A::I> struct R { };struct D: A::B, A { };

Here, all the uses ofA​::​Iare well-formed becauseA​::​f,A​::​x, and A​::​Qare members of classAandgand R are friends of classA.

This implies, for example, that access checking on the first use ofA​::​Imust be deferred until it is determined that this use ofA​::​Iis as the return type of a member of classA.

Similarly, the use of A​::​B as abase-specifier is well-formed because Dis derived from A, so checking of base-specifier_s_must be deferred until the entire base-specifier-list has been seen.

— _end example_]

Access is checked for a default argument ([dcl.fct.default]) at the point of declaration, rather than at any points of use of the default argument.

Access checking for default arguments in function templates and in member functions of class templates is performed as described in [temp.inst].

Access for a default template-argument ([temp.param]) is checked in the context in which it appears rather than at any points of use of it.

[Example 5: class B { };template <class T> class C { protected: typedef T TT;};template <class U, class V = typename U::TT> class D : public U { }; D <C<B> >* d; — _end example_]