Class declaration

 

C++

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Syntax

class identifier { class_body } object_list ;	(1)
class identifier : ancestor_list { class_body } object_list ;	(2)
class identifier ;	(3)
class identifier final opt_ancestors_and_body	(4)	(since C++11)

Class Body

A list of member and friend declarations and access specifiers:

public:	(1)
protected:	(2)
private:	(3)
friend friend_declaration	(4)
member_declaration	(5)
static member_declaration	(6)
nested_type_declaration	(7)

Ancestor List

A list of classes that have already bee fully defined optionally prefixed with an access specifier

Object List

An optional list of instances of the previously defined class

Explanation

1. Defines a class and its member
2. Defines a class inheriting other classes
3. Forwards declares a class
4. Defines a class that cannot be derived from ( see final )

If friend or member functions have their body defined inside the class body, they are implicitly inlined

Notes

(since C++11) A default value can be assigned to data members inside the class body (ie: not necessarily in a constructor)

See also

• access specifier
• friend declaration
• static members

Example

class C;
 
class D : public B // B needs to be defined
{
  private:
    C *ptr_c; // a pointer/reference to C can be used as C has been forward declared
    double x = 12.3; // C++11 inline data member initialization
    static const int sci = 1; // this is valid in C++98 as well
  public:
    typedef B parent_type;
 
    // inline function
    virtual parent_type foo() const
    {
        return B();
    }
 
    // non-inline function declaration. needs to be defined externally
    void bar();
} D_obj; // An object of type D is defined
 
// definition of a class method outside the class
void D::bar()
{
   //...
}