A class is a user-defined type.
A class can have the following kinds of members:
All members are defined at once in the class definition, they cannot be added to an already-defined class (unlike the members of namespaces).
A member of a class
T cannot use
T as its name if the member is.
However, a non-static data member may use the name
T as long as there are no user-declared constructors.
A class with at least one declared or inherited virtual member function is polymorphic. Objects of this type are polymorphic objects and have runtime type information stored as part of the object representation, which may be queried with
typeid. Virtual member functions participate in dynamic binding.
A class with at least one declared or inherited pure virtual member function is an abstract class. Objects of this type cannot be created.
Trivially copyable class
A trivially copyable class is a class that.
A trivial class is a class that.
A standard-layout class is a class that.
A standard-layout struct is a standard-layout class defined with the class keyword
An implicit-lifetime class is a class that.
Notes: the implicit-lifetime property is clarified by defect report P0593R6.
A POD class is a class that.
| ||(until C++11)|
| ||(since C++11)|
A POD struct is a non-union POD class. A POD union is a union that is a POD class.
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
|DR||Applied to||Behavior as published||Correct behavior|
|CWG 148||C++98|| POD classes could not contain pointers to member, |
which are themselves POD (scalar) types
|CWG 383||C++98|| copy assignment operators or destructors could be |
user-declared in POD classes if they are not defined
|CWG 1363||C++11|| a class that has both trivial default constructors and non-trivial |
default constructors at the same time could be trivial
|it is non-trivial|
|CWG 1496||C++11|| a class that only has constructors that |
are all defined as deleted could be trivial
|it is non-trivial|
|CWG 1672||C++11|| a class could be a standard-layout class |
if it has multiple empty base classes
|it is not a standard-layout class|
|CWG 1734||C++11|| a trivially copyable class could not have non-trivial |
deleted copy/move constructors/assignment operators
|can be trivial if deleted|
|CWG 1813||C++11|| a class was never a standard-layout class if it has a |
base class that inherits a non-static data member
|it can be a standard-layout class|
|CWG 1881||C++11|| for a standard-layout class and its base classes, |
unnamed bit-fields might be declared in a
different class declaring the data members
| all non-static data members
and bit-fields need to be first
declared in the same class
|CWG 1909||C++98||a member template could have the same name as its class||prohibited|
|CWG 2120||C++11|| the definition of M(X) in determining a standard- |
layout class did not consider the case of
a class whose first member is an array
| addressed this case in
the definition of M(X)
|CWG 2605||C++98||an implicit-lifetime class could have a user-provided destructor||prohibited|
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