C++ classes

A class in C++ is a user defined type or data structure declared with keyword class that has data and functions (also called methods) as its members whose access is governed by the three access specifiers private, protected or public (by default access to members of a class is private). The private members are not accessible outside the class; they can be accessed only through methods of the class. The public members form an interface to the class and are accessible outside the class.

Instances of a class data type are known as objects and can contain member variables, constants, member functions, and overloaded operators defined by the programmer.

In C++, a class defined with the class keyword has private members and base classes by default. A structure is a class defined with the struct keyword. Its members and base classes are public by default. This is the only difference between structs and classes in the C++.

An aggregate class is a class with no user-declared constructors, no private or protected non-static data members, no base classes, and no virtual functions. Such a class can be initialized with a brace-enclosed comma-separated list of initializer-clauses. The following code has the same semantics in both C and C++.

A POD-struct (Plain Old Data Structure) is an aggregate class that has no non-static data members of type non-POD-struct, non-POD-union (or array of such types) or reference, and has no user-defined assignment operator and no user-defined destructor. A POD-struct could be said to be the C++ equivalent of a C struct. In most cases, a POD-struct will have the same memory layout as a corresponding struct declared in C. For this reason, POD-structs are sometimes colloquially referred to as "C-style structs".

C++ classes have their own members. These members include variables (including other structures and classes), functions (specific identifiers or overloaded operators) known as methods, constructors and destructors. Members are declared to be either publicly or privately accessible using the public: and private: access specifiers respectively. Any member encountered after a specifier will have the associated access until another specifier is encountered. There is also inheritance between classes which can make use of the protected: specifier.

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