C++面向对象程序设计双语教程（第3版）课件 class 8-operator overloading-1

ObjectivesToknowwhyneedsoperatoroverloadingToknowwhatoperatorfunctionsareTo

be

abletodefinebinaryoperatorfunctionTobeabletodefineunaryoperatorfunction01Introduction03BinaryOperatorOverloading02OperatorFunctions04UnaryOperatorOverloading05CaseStudy01IntroductiontoOperatorOverloadingIntroductiontoOperatorOverloadingForexample,built-inoperators,+,-,=,<=,[],>>,<<2+3,3.4+5.4,‘a’+’b’Usingthesamenameforoperationsondifferenttypesisknownasoverloading.Operatoroverloading:Redefinemostofthebuilt-inoperatorsavailableforoperationson

user-definedtypes(abstractdatatypes).class

MyInteger{public:MyInteger(int=0);intget()const;MyIntegeraddition(const

MyInteger&);MyIntegermultiplication(const

MyInteger&);private:intvalue;};WhyNeedsOperatorOverloading?MyIntegervalue:int+MyInteger(int=0)+~MyInteger()+addition(constMyInteger&):MyInteger+multiplication(constMyInteger&):MyInteger+get():intconstCaseStudy1DefineaMyIntegerclasswithavalueattribute.Youneeddothefollowingtask:addtwoMyIntegerobjectsmultiplytwoMyIntegerobjectsWhyNeedsOperatorOverloading?intmain(){MyIntegeri1(10),i2(25);cout<<i1.get()<<

","

<<i2.get()<<endl;MyIntegeri3;i3=i1.addition(i2);cout<<i3.get()<<endl;i3=i1.multiplication(i2);cout<<i3.get()<<endl;return0;}i3=i1+i2;i3=i1*i2;MyInteger

MyInteger::addition(const

MyInteger&myint){return

MyInteger(this->value+myint.value);}MyInteger

MyInteger::multiplication(const

MyInteger&myint){return

MyInteger(this->value*myint.value);}MyInteger::MyInteger(int

v):value(v){}int

MyInteger::get()const{returnvalue;}MyInteger::~MyInteger(){}MyIntegervalue:int+MyInteger(int=0)+~MyInteger()+addition(constMyInteger&):MyInteger+multiplication(constMyInteger&):MyInteger+get():intconstWhyNeedsOperatorOverloading?Definingoperatorsforuser-definedtypeallowsaprogrammertoprovideamoreconventionalandconvenient

notationformanipulatingobjects.MyIntegeri3;i3=i1+i2;i3=i1*i2;intn;cin>>n;cout<<n;class

MyInteger{public:MyInteger(int=0);intget()const;MyInteger

operator+(const

MyInteger&);MyInteger

operator*(const

MyInteger&);private:intvalue;};OperatoroverloadingFunctionMyInteger

MyInteger::operator+(const

MyInteger&myint){return

MyInteger(this->value+myint.value);}MyInteger

MyInteger::operator*(const

MyInteger&myint){return

MyInteger(this->value*myint.value);}intmain(){MyIntegeri1(10),i2(25);cout<<i1.get()<<

","

<<i2.get()<<endl;MyIntegeri3;i3=i1+i2;//i3=i1.addition(i2);cout<<i3.get()<<endl;i3=i1*i2;//i3=i1.multiplication(i2);cout<<i3.get()<<endl;return0;}WhyNeedsOperatorOverloading?MyIntegervalue:int+MyInteger(int=0)+~MyInteger()+operator+(constMyInteger&):MyInteger+operator*(constMyInteger&):MyInteger+get():intconst02OperatorFunctionsOperatorFunctionsMyIntegeroperator+(constMyInteger&myint);returningtypeoperatorfunctionnameparameterlistForexample,Tooverloadanoperator,youmustdefineafunction,calledoperatoroverloadingfunction(operatorfunction).returning-typeoperatorSymbol(parameter

list)SyntaxtodefineanoperatorfunctionoperatorfunctionnameOperatorFunctionsThefollowingoperatorscanbeoverloaded.Thefollowingoperatorscannotbeoverloaded.::---scoperesolution,e.g.Date::print();?:---ternaryconditional(if-then-else),e.g.x>y?x:y;.---memberselection,e.g.day.print();.*---memberselectionthroughpointertomember,e.g.student.*nameOperatorFunctionsYoucannotoverloadalloperators.Youcannotcreateanewoperator.Onlyexistingoperatorcanbeoverloaded.Youtrytokeepthemeaningofhowtheoperatorworkswithbuilt-intypes.Operatorfunctionscanbememberfunctionsofclassesornon-member

functions.

03BinaryOperatorOverloadingBinaryOperatorsForexample,+,-,==,!=,&&Abinaryoperatorisanoperatorthatoperatesontwooperandsandmanipulatesthemtoreturnaresult.HowtoOverloadBinaryOperatorsForanybinaryoperator@,

aa@bb

MyInteger

MyInteger::operator+(MyInteger&i);MyInteger

operator+(MyInteger&i1,MyInteger&i2);Object’snames,user-definedtypeintmain{MyIntegeri1(10),i2(25),i3;i3=i1+i2;i3=i1*i2;}SyntaxtodefineabinaryoperatorfunctionIfanoperatorfunctionisdefinedasamemberfunction,

ittakesoneparameter.TherearetwowaystodefineanoperatorfunctionIfanoperatorfunctionisdefinedasanon-memberfunction,

ittakestwoparameters.aa.operator+(bb)operator+(aa,bb)HowtoOverloadBinaryOperatorsclass

MyInteger{public:MyInteger(int

v):value(v){}MyIntegeroperator+(MyInteger&);friend

MyIntegeroperator-(MyInteger&,MyInteger&);intget()const{returnvalue;}private:intvalue;};memberfunctionnon-memberfunctionintmain(){MyIntegera(13);MyIntegerb(12);MyIntegerc=b;//copyconstructora=b+c;b=b+c-a;cout<<a.get()<<b.get();return0;}MyInteger

MyInteger::operator+(MyInteger&i){MyIntegertemp(0);temp.value=this->value+i.value;returntemp;}MyIntegeroperator-(MyInteger&i1,MyInteger&i2){MyIntegertemp(0);temp.value=i1.value-i2.value;returntemp;}a=b.operator+(c)b=operator-(b.operator+(c),a)04UnaryOperatorOverloadingUnaryOperatorsForexample,++a,--a,a--,a++,a−(−b),~a,!aAnunaryoperatorisanoperatorthatactsuponasingleoperandtoproduceanewvalue.HowtoOverloadUnaryOperatorsForanyprefixunaryoperator@@aaDefinitionofprefix

increment/decrementoperatorsObject’sname，user-definedtypeintmain{MyIntegeri1(10),i2(25);++i1;--i2;cout<<(++i1).get()<<endl;}MyInteger&MyInteger::operator++();MyInteger

operator--(MyInteger&);SyntaxtodefineanunaryoperatorfunctionIfanoperatorfunctionisdefinedasamemberfunction,

itdoesnottakeanyparameter.TherearetwowaystodefineanoperatorfunctionIfanoperatorfunctionisdefinedasanon-memberfunction,

ittakesoneparameter.aa.operator++()operator--(aa)PrefixUnaryOperatorsclass

MyInteger{public:MyInteger(int);intget()const;MyInteger&operator++();//memberfunctionfriend

MyInteger

operator--(MyInteger&);//non-memberfunctionprivate:intvalue;};intmain(){MyIntegeri1(10),i2(25);cout<<i1.get()<<

","

<<i2.get()<<endl;cout<<(++i1).get()<<endl;cout<<(--i2).get()<<endl;return0;}MyInteger&MyInteger::operator++(){

this->value++;

return*this;}(i1.operator++()).get()(operator--(i2)).get()MyInteger

operator--(MyInteger&myint){

myint.value--;return

myint;}PrefixunaryoperatorsWhytoreturnthethispointer?PostfixUnaryOperatorsForanypostfixunaryoperator@aa@Definitionofpostfixincrement/decrementoperatorsObject’sname,user-definedtypeintmain(){MyIntegeri1(10),i2(25);i1++;i2++;cout<<(i1++).get()<<endl;}SyntaxtodefineanunaryoperatorfunctionIfanoperatorfunctionisdefinedasamemberfunction,

itdoesnottakeanyparameter,butidentifierint.TherearetwowaystodefineanoperatorfunctionIfanoperatorfunctionisdefinedasanon-memberfunction,

ittakesoneparameterandidentifierint.MyInteger

MyInteger::operator++(int);MyInteger

operator--(MyInteger&,int);Note:intisadummyparameteraa.operator++(int)operator--(aa,int)PostfixUnaryOperatorsintmain(){MyIntegeri1(10),i2(25);cout<<i1.get()<<

","

<<i2.get()<<endl;cout<<(i1++).get()<<endl;cout<<i1.get()<<endl;cout<<(i2--).get()<<endl;cout<<i2.get()<<endl;return0;}class

MyInteger{public:MyInteger(int);intget()const;MyInteger

operator++(int);//memberfunctionfriend

MyInteger

operator--(MyInteger&,int);private:intvalue;};(i1.operator++(int)).get()(operator--(i2,int)).get()postfixunaryoperatorsMyInteger

MyInteger::operator++(int){MyIntegertemp(0)=*this;this->value++;returntemp;}MyInteger

operator--(MyInteger&myint,int){MyIntegertemp(0)=myint;myint.value--;returntemp;}05CaseStudyCaseStudyGivenatestprogramasfollows.DefineaComplexclassaccordingtothetestprogram.a+biComplexreal:doubleimag:double+Complex(double=0,double=0)+~Complex()+Complex(constComplex&)+operator+(constComplex&):Complex+operator=(constComplex&):Complex&+operator++():Complex&+operator++(int):Complex+print():voidconstintmain(){Complexc1(2.1,4.5),c2(3.4,5.6);c1.print();c2.print();Complexc3=c1+c2;c3.print();c1=c3;c1.print();(++c3).print();(c3++).print();c3.print();return0;}DefinitionoftheComplexclassWhendoyouneedtopassavalueorareferencetoanoperatorfunction?Whendoyouneedtoreturnavalueorareferencefromanoperatorfunction?class

Complex{public:Complex(double

r=0,double

i=0);//defaultconstructorComplex(const

Complex&);//copyconstructorComplex

operator+(Complex&);//operator+Complex&operator=(Complex&);//operator=Complex&operator++();//prefixoperator++friend

Complex

operator++(Complex&,int);//postfixoperator++voidprint()const;private:doublereal,imag;};Complexreal:doubleimag:double+Complex(double=0,double=0)+~Complex()+Complex(constComplex&)+operator+(constComplex&):Complex+operator=(constComplex&):Complex&+operator++():Complex&+operator++(int):Complex+print():voidconstBinaryandUnaryOperatorFunctionsComplex

Complex::operator+(Complex&c){return

Complex(this->real+c.real,this->imag+c.imag);}class

Complex{public:Complex(double

r=0,double

i=0);//defaultconstructorComplex(const

Complex&);//copyconstructorComplex

operator+(Complex&);//operator+Complex&operator=(Complex&);//operator=Complex&operator++();//prefixoperator++friend

Complex

operator++(Complex&,int);//postfixoperator++voidprint()const;private:doublereal,imag;};Complex&Complex::operator++(){this->real++