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Classes, Structures, and Unions

This section introduces C++ classes. Classes, which can contain data and functions, introduce user-defined types into a program. User-defined types in traditional programming languages are collections of data which, taken together, describe an object's attributes and state. Class types in C++ enable you to describe attributes and state, and to define behavior.

The following topics are included:

The three class types are structure, class, and union. They are declared using the struct, class, and union keywords (see the class-key grammar in Defining Class Types). The following table shows the differences among the three class types.

Access Control and Constraints of Structures, Classes, and Unions

Structures Classes Unions
class-key is struct class-key is class class-key is union
Default access is public Default access is private Default access is public
No usage constraints No usage constraints Use only one member at a time

See Also

C++ Language Reference

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