Constructors for classes · Default Parameterized Copy Destructors Overloading constructors Member...

Initializationreview

Definitions

Types ofconstructor

Default

Parameterized

Destructors

Overloadingconstructors

Memberinitializationlists

Initialize fromexisting object

Copy constructor

Operator=

Classes inclasses

Constructors for classes

Comp Sci 1570 Introduction to C++

Definitions

Types ofconstructor

Default

Parameterized

Destructors

Copy constructor

Operator=

Classes inclasses

Outline

1 Initialization review

2 Definitions

3 Types of constructorDefaultParameterizedCopyDestructors

4 Overloading constructors

5 Member initialization lists

6 Initialize from existing objectCopy constructorOperator=

7 Classes in classes

Definitions

Types ofconstructor

Default

Parameterized

Destructors

Copy constructor

Operator=

Classes inclasses

C++ supports several basic ways to initialize

i n t nValue ; // d e c l a r e but not d e f i n enValue = 5 ; // a s s i g n

i n t nValue = 5 ; // copy i n i t i a l i z a t i o n

i n t nValue ( 5 ) ; // d i r e c t i n i t i a l i z a t i o n

i n t v a l u e {5} ; // un i fo rm i n i t . (C++ 11 on l y )

MyClass m y o b j e c t ; // d e c l a r e but not d e f i n e// i n i t i a l i z a t i o n ?

Even though direct initialization form looks a lot like a functioncall, the compiler keeps track of which names are variables andwhich are functions. Direct initialization can perform betterthan copy initialization for some data types. It also helpsdifferentiate initialization from assignment.

Definitions

Types ofconstructor

Default

Parameterized

Destructors

Copy constructor

Operator=

Classes inclasses

Outline

2 Definitions

Definitions

Types ofconstructor

Default

Parameterized

Destructors

Copy constructor

Operator=

Classes inclasses

Constructors

To be able to initialize your user-defined types, you must writea special kind of member function for your class. It is called aconstructor. Constructors are really rather special in that theyhave some key features:

• Constructors are always named the name of the class(with the same capitalization)

• Constructors have no return type (not even void) andhence has no return statement.

• Constructors can be overloaded like any other function,and you will most likely do so.

• Constructors are called by the compiler automatically; theyare rarely called explicitly by the programmer.

• If you write no constructor, the compiler will provide yourclass with a default constructor. The mechanism issuppressed once you write any constructor.

Definitions

Types ofconstructor

Default

Parameterized

Destructors

Copy constructor

Operator=

Classes inclasses

Outline

2 Definitions

Definitions

Types ofconstructor

Default

Parameterized

Destructors

Copy constructor

Operator=

Classes inclasses

Outline

2 Definitions

Definitions

Types ofconstructor

Default

Parameterized

Destructors

Copy constructor

Operator=

Classes inclasses

Default constructor

A constructor that accepts no parameters is known as defaultconstructor. If no constructor is defined then the compilersupplies a default constructor.

C i r c l e : : C i r c l e ( ){

r a d i u s = 0 ;}

i n t main ( ){C i r c l e m y c i r c l e ;m y c i r c l e . r a d i u s =4;

Definitions

Types ofconstructor

Default

Parameterized

Destructors

Copy constructor

Operator=

Classes inclasses

Outline

2 Definitions

Definitions

Types ofconstructor

Default

Parameterized

Destructors

Copy constructor

Operator=

Classes inclasses

Parameterized constructor

A constructor that receives arguments/parameters, is calledparameterized constructor.

C i r c l e : : C i r c l e ( double r ){

r a d i u s = r ;}

i n t main ( ){C i r c l e m y c i r c l e ( 4 ) ;

Definitions

Types ofconstructor

Default

Parameterized

Destructors

Copy constructor

Operator=

Classes inclasses

Outline

2 Definitions

Definitions

Types ofconstructor

Default

Parameterized

Destructors

Copy constructor

Operator=

Classes inclasses

Copy constructor

A constructor that initializes an object using values of anotherobject passed to it as parameter, is called copy constructor. Itcreates the copy of the passed object.

C i r c l e : : C i r c l e ( C i r c l e &o t h e r C i r c l e ){

r a d i u s = o t h e r C i r c l e . r a d i u s ;}

i n t main ( ){C i r c l e m y c i r c l e ( 4 ) ;C i r c l e m y c i r c l e 2 ( m y c i r c l e ) ;

Definitions

Types ofconstructor

Default

Parameterized

Destructors

Copy constructor

Operator=

Classes inclasses

Outline

2 Definitions

Definitions

Types ofconstructor

Default

Parameterized

Destructors

Copy constructor

Operator=

Classes inclasses

Destructors

A destructor is a member function having sane name as that ofits class preceded by (tilde) sign and which is used to destroythe objects that have been created by a constructor. It getsinvoked when an object’s scope is over.

˜ C i r c l e ( ) {}

We don’t cover these this semester

Definitions

Types ofconstructor

Default

Parameterized

Destructors

Copy constructor

Operator=

Classes inclasses

Outline

2 Definitions

Definitions

Types ofconstructor

Default

Parameterized

Destructors

Copy constructor

Operator=

Classes inclasses

Overloading constructors

Like any other function, a constructor can also be overloadedwith different versions taking different parameters: with adifferent number of parameters and/or parameters of differenttypes. The compiler will automatically call the one whoseparameters match the arguments

Definitions

Types ofconstructor

Default

Parameterized

Destructors

Copy constructor

Operator=

Classes inclasses

Outline

2 Definitions

Definitions

Types ofconstructor

Default

Parameterized

Destructors

Copy constructor

Operator=

Classes inclasses

Member initialization lists

• When a constructor is used to initialize other members,these other members can be initialized directly, withoutresorting to statements in its body, by inserting, before theconstructor’s body, a colon (:) and a list of initializationsfor class members.

• For members that cannot be default-initialized, such asmembers of reference and const-qualified types, memberinitializers must be specified.

• If non-static const data members in your class have defaultconstructors and you don’t use a constructor initializer list,you won’t be able to initialize them to intended state asthey will be initialized to their default state.

• Reference data members must be intialized when compilerenters constructor as references can’t be just declared &initialized later. This is possible only with constructorinitializer list.

• Efficiency: rather than calling default init just to overwritelater, initialize directly

Definitions

Types ofconstructor

Default

Parameterized

Destructors

Copy constructor

Operator=

Classes inclasses

Member initialization lists

c l a s s R e c t a n g l e{

i n t width , h e i g h t ;pub l i c :

R e c t a n g l e ( int , i n t ) ;i n t a r e a ( ){ return width ∗ h e i g h t ;}

R e c t a n g l e : : R e c t a n g l e ( i n t x , i n t y ){width=x ; h e i g h t=y ;}// orR e c t a n g l e : : R e c t a n g l e ( i n t x , i n t y ) : w idth ( x ){ h e i g h t=y ;}// orR e c t a n g l e : : R e c t a n g l e ( i n t x , i n t y ) :w idth ( x ) , h e i g h t ( y ){ }

Definitions

Types ofconstructor

Default

Parameterized

Destructors

Copy constructor

Operator=

Classes inclasses

Outline

2 Definitions

Definitions

Types ofconstructor

Default

Parameterized

Destructors

Copy constructor

Operator=

Classes inclasses

Outline

2 Definitions

Definitions

Types ofconstructor

Default

Parameterized

Destructors

Copy constructor

Operator=

Classes inclasses

Copy constructor

c l a s s MyClass{

pub l i c :i n t a , b ; s t r i n g c ;

MyClass : : MyClass ( const MyClass& e x i s t i n g O b j ) :a ( x . a ) , b ( x . b ) , c ( x . c ) {}

i n t main ( ){MyClass

Definitions

Types ofconstructor

Default

Parameterized

Destructors

Copy constructor

Operator=

Classes inclasses

Outline

2 Definitions

Definitions

Types ofconstructor

Default

Parameterized

Destructors

Copy constructor

Operator=

Classes inclasses

Operator= provided by default (copy assignment)

MyClass f o o ;

// ob j e c t i n i t i a l i z a t i o n : copy c o n s t r u c t o rMyClass bar ( f o o ) ;

// ob j e c t i n i t i a l i z a t i o n : copy c o n s t r u c t o rMyClass baz = f o o ;

// ob j e c t a l r e a d y i n i t i a l i z e d : copy as s i gnmentf o o = bar ;

Body of overloading function is similar to copy constructor

Definitions

Types ofconstructor

Default

Parameterized

Destructors

Copy constructor

Operator=

Classes inclasses

Outline

2 Definitions

Definitions

Types ofconstructor

Default

Parameterized

Destructors

Copy constructor

Operator=

Classes inclasses

Classes in classes

• A class may contain other classes as member variables.

• By default, when the outer class is constructed, themember variables will have their default constructorscalled.

• This happens before the body of the constructor executes.

Constructors for classes · Default Parameterized Copy Destructors Overloading constructors Member...

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