C++計算機語言教學課件c++-lect06operatoroverloading

Chapter5-C++OperatorOverloadingOutline5.1 Introduction5.2 FundamentalsofOperatorOverloading5.3 RestrictionsonOperatorOverloading5.4 OperatorFunctionsasClassMembersvs.asfriendFunctions5.5 OverloadingStream-InsertionandStream-ExtractionOperators5.6 OverloadingUnaryOperators 5.7 OverloadingBinaryOperators5.8 CaseStudy:AnArrayClass5.9 ConvertingbetweenTypes5.10 Overloading++and--

ObjectivesInthischapter,youwilllearn:Tounderstandhowtoredefine(overload)operatorstoworkwithnewtypes.Tounderstandhowtoconvertobjectsfromoneclasstoanotherclass.Tolearnwhento,andwhennotto,overloadoperators.Tostudyseveralinterestingclassesthatuseoverloadedoperators.TocreateanArrayclass.

4.1Introduction（1）運算符重載是對已有的運算符賦予多重含義，使同一個運算符作用于不同類型的數(shù)據(jù)時，產(chǎn)生不同類型的行為。C++允許同一運算符具有多種不同運算功能的機制。（2）為什么需要運算符重載：C++中預定義了許多運算符,能夠滿足用戶的一般應用要求,但是其運算的對象應是基本數(shù)據(jù)類型,而不適用于用戶自定義數(shù)據(jù)類型(如類),這可以使用運算符重載。（3）明智地使用操作符重載可以使類類型的使用像內置類型一樣直觀（4）操作符的實質是函數(shù)重載。4.1IntroductionOperatoroverloading

Usetraditionaloperatorswithuser-definedobjectsStraightforwardandnaturalwaytoextendC++Requiresgreatcare

Whenoverloadingismisused,programsbecomedifficulttounderstand

classpoint {public: point(intxx=0,intyy=0){x=xx;y=yy;}

intget_x();

intget_y(); //...private:

intx;

inty;};pointp1(1,1),p2(3,3)，實現(xiàn)“p1+p2”則需要編寫程序來說明“+”如何作用于point對象（p1,p2），即p1的私有成員x，y與p2的私有成員x，y分別相加這一功能。4.2FundamentalsofOperatorOverloadingUseoperatoroverloadingtoimprovereadabilityAvoidexcessiveorinconsistentusageFormatWritefunctiondefinitionasnormal(重載函數(shù)跟普通函數(shù)一樣，具有返回類型和形參表)Functionnameiskeywordoperatorfollowedbythesymbolfortheoperatorbeingoverloaded.

operator+wouldbeusedtooverloadtheadditionoperator(+).4.2FundamentalsofOperatorOverloadingAssignmentoperator(=)maybeusedwitheveryclasswithoutexplicitoverloadingmemberwiseassignment(不需專門定義，默認存在，逐一復制數(shù)據(jù)成員)class

MyClass{

public:...

MyClass&operator=(const

MyClass&rhs);...}

MyClass&MyClass::operator=(const

MyClass&rhs){...return*this;}

MyClassa,b,c;...a=b=c;//Sameasb.operator=(a);4.3RestrictionsonOperatorOverloading

MostofC++’soperatorscanbeoverloaded有四個符號（+,-,*和&）既可作一元操作符又可作二元操作符，可以同時定義一元和二元操作符重載操作符不能改變原操作符的優(yōu)先級、結合性或操作數(shù)目重載操作符必須具有至少一個自定義類類型類型的操作數(shù)，也就是說重載操作符不能重新定義用于內置類型對象的操作符的含義，比如不能重載”+”號操作符用于兩個整數(shù)相加。ExampleAnoverloadingfortheoperator“+”forthisclass

classpoint {public: point(int

xx=0,int

yy=0){x=xx;y=yy;}

int

get_x();

int

get_y();pointoperator+(constpoint&rpt);//...private:

intx;

int

y;};pointpoint::operator+(constpoint&rpt){

int

tempx=x+rpt.get_x();

int

tempy=y+rpt.get_y();pointtemp(tempx,tempy);returntemp;}ExampleAnoverloadingfortheoperator“+”forthisclass

//**include“point.h”;include<iostream>main(){pointa(15,20),b(5,13);pointtestpoint;

testpoint=a+b;

}ClasspracticeWriteanoverloadingfortheoperator“*=”forthisclass

classpoint {public: point(intxx=0,intyy=0){x=xx;y=yy;}

intget_x();

intget_y(); //...private:

intx;

inty;};pointp1(1,1),p2(3,3)，實現(xiàn)“p1*=p2”，即p1的私有成員x，y與p2的私有成員x，y分別相乘，并將結果分別賦于p1的私有成員。ClasspracticeWriteanoverloadingfortheoperator“*=”

classpoint {public: point(int

xx=0,int

yy=0){x=xx;y=yy;}

int

get_x();

int

get_y();point&operator*=(constpoint&rpt);//...private:

intx;

int

y;};point&point::operator*=(constpoint&rpt){x=x*rpt.get_x();y=y*rpt.get_y();return*this;}4.4OperatorFunctionsasClassMembersvs.asfriendFunctionsOperatorfunctionsCanbememberornon-memberfunctionsOverloadingtheassignmentoperatorsi.e:(),[],->,=Operatormustbeamemberfunction

4.4OperatorFunctionsasClassMembersvs.asfriendFunctionsOperatorfunctionsasmemberfunctionsLeftmostoperandmustbeanobject(orreferencetoanobject)oftheclassIfleftoperandofadifferenttype(與定義的class不一致),operatorfunctionmustbeanon-memberfunctionAnon-memberoperatorfunctionmustbeafriendifprivateorprotectedmembersofthatclassareaccesseddirectly如果需要訪問類的私有或者保護對象4.4OperatorFunctionsasClassMembersvs.asfriendFunctionsNon-memberoverloadedoperatorfunctionsEnabletheoperatortobecommutative(可交換的)，becausetheleftmostoperandcanbeanothertype.

HugeIntegerbigInteger1;longintnumber;bigInteger1=number+bigInteger1; orbigInteger1=biginteger1+number;4.4OperatorFunctionsasClassMembersvs.asfriendFunctionsFriendfunctionMemberFunctiona+boperator+(a,b)a.operator+(b)a++operator++(a,0)a.operator++(0)-aoperator-(a)a.operator-()類成員的操作符函數(shù)與其等價的友元函數(shù)：4.4OperatorFunctionsasClassMembersvs.asfriendFunctions友元運算符函數(shù)無this指針，因而在函數(shù)體內必須通過對象名來使用private成員數(shù)據(jù)；一般將一元運算符函數(shù)重載為成員運算符函數(shù)。強調：與賦值相關的運算符必須重載成成員函數(shù)。一般將二元運算符重載為友元運算符函數(shù)，以免出現(xiàn)使用錯誤。因為時常需要操作數(shù)可交換“=”、“（）”、“[]”和“->”不能重載為友元。4.5OverloadingStream-InsertionandStream-ExtractionOperators

Overloaded<<

and

>>operatorsMusthaveleftoperandoftypesostream&,istream&respectivelyItmustbe

anon-memberfunction(leftoperandnotanobjectoftheclass)Itmustbeafriendfunctionifitaccessesprivatedatamembers注意：在本課程學習的OperatorOverloading中，通過non-memberfunction來定義operator，就是指用friendfunction來實現(xiàn)fig18_03.cpp(1of3)語法：friend<函數(shù)類型>operator<運算符>(形參表){函數(shù)體；}fig18_03.cpp(2of3)fig18_03.cpp(3of3)Enterphonenumberintheform(123)456-7890:(800)555-1212Thephonenumberenteredwas:(800)555-12124.6OverloadingUnaryOperatorsOverloadingunaryoperatorsAvoid

friendfunctionsandfriendclassesunlessabsolutelynecessary.Useoffriendsviolatestheencapsulationofaclass.Asamemberfunction:classString{

public:

booloperator!()const;

...

};<函數(shù)類型>operator<運算符>(形參表){函數(shù)體；}4.7OverloadingBinaryOperatorsOverloadedbinaryoperatorsNon-staticmemberfunction,oneargumentNon-memberfunction(friend),twoarguments

classString{

public:

constString&operator+=(constString&);

...

};//endclassString

y+=z;

equivalenttoy.operator+=(

z

);4.7OverloadingBinaryOperatorsExampleclassString{friend

constString&operator+=(String&,constString&);...};//endclassString

y+=z;equivalent

to

operator+=(

y,

z

);語法：friend<函數(shù)類型>operator<運算符>(形參表){函數(shù)體；}4.8CaseStudy:AnArrayclassImplementanArrayclasswith

RangecheckingArrayassignmentArraysthatknowtheirsizeOutputting/inputtingentirearrayswith<<and>>Arraycomparisonswith==and!=array1.h(1of2)array1.h(2of2)array1.cpp(1of6)array1.cpp(2of6)array1.cpp(3of6)array1.cpp(3of6)array1.cpp(4of6)array1.cpp(5of6)array1.cpp(6of6)fig18_04.cpp(1of4)fig18_04.cpp(2of4)fig18_04.cpp(3of4)fig18_04.cpp(4of4)Arrayoutput(1of1)#ofarraysinstantiated=0#ofarraysinstantiated=2

Sizeofarrayintegers1is7Arrayafterinitialization:0000000

Sizeofarrayintegers2is10Arrayafterinitialization:0000000000Input17integers:1234567891011121314151617Afterinput,thearrayscontain:integers1:1234567integers2:891011121314151617

Evaluating:integers1!=integers2Theyarenotequal

Sizeofarrayintegers3is7Arrayafterinitialization:1234567Arrayoutput(2of2)Assigningintegers2tointegers1:integers1:891011121314151617integers2:891011121314151617Evaluating:integers1==integers2Theyareequal

integers1[5]is13Assigning1000tointegers1[5]integers1:89101112100014151617

Attempttoassign1000tointegers1[15]Assertionfailed:0<=subscript&&subscript<size,fileArray1.cpp,line95abnormalprogramtermination4.9ConvertingbetweenTypesCastoperatorConvertobjectsintobuilt-intypesorotherobjectsConversionoperatormustbeanon-static

memberfunction.Cannotbeafriendfunction形參表必須為空不能指定返回類型，但是必須顯式返回一個指定類型的值轉換函數(shù)采用如下通用形式：operatortype();type表