CppClass.md

(C++) class

class is a keyword to start a class declaration. A class is a user-defined data type for a concept There are multiple class access levels. There are multiple class types. There are multiple class examples.

'A class is a user-defined data type which consists of data elements and functions which operate on that data. In C++, this may be declared as a class; it may also be declared as a struct or a union. Data defined in a class is called member data and functions defined in a class are called member functions.' [2]

Class elements are:

• constructor
• copy assignment operator
• destructor
• members
• helper functions

The class keyword also be used to create a template function.

Example class

class my_class
{
  public: int m_value;
};

int main()
{
  my_class m;
  m.m_value = 10;
}
``` 

## ![C++98](PicCpp98.png)![C++11](PicCpp11.png) [Class](CppClass.md) elements

A [class](CppClass.md) can have many types of [members](CppMember.md):

-   [member functions](CppMemberFunction.md) or member [functions](CppFunction.md), of which the [Big Four](CppBigFour.md) are especially important
-   [data members](CppDataMember.md) or member [variables](CppVariable.md)
-   member constants
-   member types

 

class my_class { public: void set_x(const int x) { m_x = x; } //A member function int m_x; //A data member };

 

All [classes](CppClass.md) have a four special methods called the [Big
Four](CppBigFour.md): [default constructor](CppDefaultConstructor.md),
[destructor](CppDestructor.md), [copy
constructor](CppCopyConstructor.md) and [copy assignment
operator](CppCopyAssignmentOperator.md):

struct no_class {}; //Do all classes really have a constructor, destructor, //copy constructor and copy-assignment operator?

 
This class called `no_class` is silently converted by your
[compiler](CppCompiler.md) to the following (from \[1\]):

struct no_class { no_class() //Default constructor
{ //something } no_class(const no_class& rhs) //copy constructor { //something } ~no_class() //Default destructor { //something } no_class& operator=(const no_class& rhs) //copy-assignment operator { //something } };

## [Advice](CppAdvice.md)

-   Prefer class and use struct only for helper types with limited functionality and without invariants [5]
-   Know what functions C++ silently writes and calls [1]
-   Forgetting the semicolon at the end of a [class](CppClass.md)
    [definition](CppDefinition.md) is a [syntax
    error](CppSyntaxError.md) [3]
-   Class names should be in UpperCamelCase [4]


## [References](CppReferences.md)

1.  [Scott Meyers](CppScottMeyers.md). Effective C++ (3rd edition).
    ISBN: 0-321-33487-6. Item 5: 'Know what functions C++ silently
    writes and calls'
2.  Joint Strike Fighter Air Vehicle C++ Coding Standards for the System
    Development and Demonstration Program. Document Number 2RDU00001
    Rev C. December 2005. 4.3.5: 'A class is a user-defined data type
    which consists of data elements and functions which operate on
    that data. In C++, this may be declared as a class; it may also be
    declared as a struct or a union. Data defined in a class is called
    member data and functions defined in a class are called member
    functions.'
3.  Paul Deitel, Harvey Deitel. C++11 for programmers (2nd edition).
    2014. ISBN: 978-0-13-343985-4. Chapter 3.1, Common Programming
    Error 3.1. page 39: 'Forgetting the semicolon at the end of a class
    definition is a syntax error.'
4.  Trevor Misfeldt, Gregory Bumgardner, Andrew Gray. The elements of
    C++ style. 2004. ISBN: 978-0-521-89308-4. Chapter 4.2, page 18: 'Use
    UpperCamelCase for classes, constants, structures, enumerations, and
    typedefs'
5.  Gottschling, Peter. Discovering Modern C++: An Intensive Course for Scientists, Engineers, and Programmers. Addison-Wesley Professional, 2015.
    Chapter 2.2.2.1: 'Prefer class and use struct only for helper types with limited functionality and without invariants'