StandardLayoutType

Specifies that a type is standard layout type. Standard layout types are useful for communicating with code written in other programming languages.

Note, that the standard doesn't define a named requirement or concept with this name. This is a type category defined by the core language. It is included here as concept only for consistency.

Requirements

• All non-static data members have the same access control
• Has no virtual functions or virtual base classes
• Has no non-static data members of reference type
• All non-static data members and base classes are themselves standard layout types

• Either
  • has no base classes with non-static data members, or
  • has no non-static data members in the most derived class and at most one base class with non-static data members
• Has no base classes of the same type as the first non-static data member (see empty base optimization)

(until C++14)

• Has no two base class subobjects of the same type

struct Q {}; struct S : Q { }; struct T : Q { }; struct U : S, T { }; // not a standard-layout class

• Has all non-static data members declared in the same class (either all in the derived or all in some base)

struct B { int i; }; // standard-layout class struct C : B { }; // standard-layout class struct D : C { }; // standard-layout class struct E : D { char : 4; }; // not a standard-layout class

• None of the base class subobjects has the same type as
  • for non-union types, as the first non-static data member (see empty base optimization), and, recursively, the first non-static data member of that data member if it has non-union class type, or all non-static data members of that data member if it has union type, or an element of that data member if it has array type, etc.
  • for union types, as any non-static data members, and, recursively, the first non-static data member of every member of non-union class type, and all non-static data members of all members of union type, and element type of all non-static data members of array type, etc.
  • for array types, as the type of the array element, and, recursively, the first non-static data member of the array element if it has non-union class type, or as any non-static data member of the array element if it has union type, or as the element type of the array element if it has array type, etc.

(since C++14)

Properties

See Standard layout.

Defect reports

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

See also

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http://en.cppreference.com/w/cpp/concept/StandardLayoutType