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COMS 261Computer Science I

Title: Classes

Date: November 7, 2005

Lecture Number: 28

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Announcements

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Review

• Classes– User defined data types

– Constructors• Default

– Constructors• With parameters

– Constructors• Parameters with default values

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Outline

• Classes– Copy constructor

Classes

• Copy constructor– VEC v1(1.2f, 3.4f);

– VEC v2(v1);• Uses the copy constructor• Creates v2, an independent object that contains

a copy of the data members of v1

v1.x = 1.2;

v1.y = 3.4;

v2.x = 1.2;

v2.y = 3.4;

Same values asv1, but a differentobject

Copy Constructor

– Syntax error when compiling• VEC::VEC(VEC v) { … }

– Since, call by value requires we make a copy of the vector v when calling the copy constructor

– The copy constructor would be called over and over

int main () {VEC v1;VEC v2(v1); Call the copy constructor

Call by value make a copy of v1

Copy Constructor

• Copy constructor cannot us call by value

–Only other choice is call by reference• VEC::VEC(VEC& v) { … }

–Should the copy constructor ever change the data member values of the reference parameter?• No, it should only read the values but not

change them

• Make the parameter a const reference

Copy Constructor

• vec.h: definition file

• vec.cpp: implementation file

• Caution– If you don’t provide an implementation of the

copy constructor, the compiler will supply one• It may not do what you think it will

Run CodeWarrior vec01

Assignment Operator

• It would be nice to assign one VEC object to another– v1 = v2;

• To do this we must overload the assignment operator (=) to define a function when a VEC object is on both the lhs and the rhs

Assignment Operator

• Should there be any arguments?– Yes, the VEC we wish to assign

– Avoid making a copy, use call by reference

• Should the assignment operator change the RHS?– No, make it a const reference

– VEC& operator=(const VEC& v);

Run CodeWarrior vec03

Assignment Operator

• The assignment operator for this class does not behave the way the primitive data types do– They allow chaining

• A = B = C;

– What happens if we try to chain the VEC assignment operator?

– How do we get around this?