1 COMS 261 Computer Science I Title: Classes Date: November 7, 2005 Lecture Number: 28

2 Announcements

3 Review Classes –User defined data types –Constructors Default –Constructors With parameters –Constructors Parameters with default values

4 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 as v1, but a different object

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?