---
title: "Classes and Structs (C++) | Microsoft Docs"
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---This section introduces C++ classes and structs. The two constructs are identical in C++ except that in structs the default accessibility is public, whereas in classes the default is private.
Classes and structs are the constructs whereby you define your own types. Classes and structs can both contain data members and member functions, which enable you to describe the type's state and 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 Defining Class Types). The following table shows the differences among the three class types.
For more information on unions, see Unions. For information on managed classes and structs, see Classes and Structs.
| 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 |