C++面向对象程序设计双语教程（第3版）课件 class 6-classes objects-3

ObjectivesToabletodefineconstmemberfunctionsandconstobjectsTobeabletounderstandthethispointerToabletodefineandusestaticmembersTo

managedynamicmemorybyusingnewanddelete01ConstantMemberFunctionsandConstantObjects03StaticMembers02Thethispointers04FreeStore01ConstantMemberFunctionandConstantObjectsclass

Date{public:Date(int=2018,int=1,int=1);voidoutput();intgetDay()const;intgetMonth()const;~Date();private:intday,month,year;boolcheck();};ConstantMemberFunctionsConstantmemberfunctionsclass

Date{public:Date(int=2021,int=1,int=1);voidoutput();intgetDay();intgetMonth();~Date();private:intday,month,year;boolcheck();};int

Date::getMonth(){returnmonth;}int

Date::getDay(){returnday;}Definition：Usingkeywordconstdefinesconstantmemberfunctions.Theconstkeywordisplacedaftertheparameterlistinthe

functiondeclarationanddefinition.Thosefunctionsthatdonotmodifythedataofaclass,i.e.read-only,aredefinedasconstantmemberfunction.ConstantMemberFunctionsclass

Date{public:Date(int=2018,int=1,int=1);voidoutput();intgetDay()const;intgetMonth()const;~Date();private:intday,month,year;boolcheck();};int

Date::getMonth()const{returnmonth;}int

Date::getDay()const{returnday;}intmain(){Datetoday(2021,9,15);today.output();cout<<"Date:"<<today.getMonth()<<"-"<<today.getDay();return0;}int

Date::getMonth()const{

return++month;

}//errorConstantObjectsintmain(){Datetoday(2018,9,15);today.output();cout<<"Date:"<<today.getDay()<<endl;const

Dateday;//day.output();//errorcout<<"Date:"<<day.getDay()<<endl;return0;}constantobjectclass

Date{public:Date(int=2018,int=1,int=1);voidoutput();intgetDay()const;};Non-constantobjectAn

object

of

a

class

may

be

declaredtobeconst,justlikeanyotherC++variable.ConstantObjectsintmain(){Datetoday(2018,9,15);today.output();cout<<"Date:"<<today.getDay();const

Dateday;//day.output();//errorcout<<"Date:"<<day.getDay();return0;}Aconstmemberfunctioncanbeinvokedforbothconstantandnon-constantobjectsAnon-constmemberfunctioncanbeinvokedonlyfornon-constantobjectsTheconstpropertyofanobjectgoesintoeffectaftertheconstructorfinishesexecutingandendsbeforetheclass'sdestructorexecutes.Sotheconstructoranddestructorcanmodifythedatamembersoftheobject,butothermethods(i.e.functions)oftheclasscannot.02ThethisPointersThethisPointersThe

this

pointerisapointeraccessibleonlywithinthenon-staticmemberfunctionsofa

class.Thethispointerpointstotheobjectforwhichthefunctionwasinvoked.Butanobject’sthispointerisnotpartoftheobjectitself.thisisnotanordinaryvariablebecauseitisnon-modifiable-assignmentstothisarenotallowed.CaseStudy1:defineaDateclassThethisPointersvoid

Date::output(){cout<<

this->year<<

"-"

<<

this->month<<

"-"

<<

this->day<<endl;}class

Date{public:Date(int=2018,int=1,int=1);voidoutput();intgetDay()const;voidprintThis();private:intday,month,year;boolcheck();};void

Date::printThis(){cout<<

this

<<endl;}int

Date::getDay()const{return

this->day;}intmain(){Dateday1(2021,9,15);cout<<&day1<<endl;day1.printThis();cout<<

"Sizeoftheobject:"

<<

sizeof(day1)<<endl;Dateday2(2020,9,15);cout<<&day2<<endl;day2.printThis();cout<<

"Sizeoftheobject:"

<<

sizeof(day2)<<endl;return0;}001BFDC4001BFDC4Sizeoftheobject:12001BFDB0001BFDB0Sizeoftheobject:12ThethisPointersclass

Date{public:Date(int=2018,int=1,int=1);voidoutput();Date&reset(int,int,int);intgetDay()const;~Date();private:intday,month,year;boolcheck();};Date&Date::reset(int

y,int

m,int

d){this->year=y;this->month=m;this->day=d;return*this;}intmain(){Datetoday(2018,10,15);today.output();cout<<"Date:"<<(today.reset(2021,9,20)).getDay()<<endl;return0;}2018-10-15Date:20ObjectisdestroyedDate::~Date(){cout<<"Objectisdestroyed\n";}CaseStudy1-1:defineaDateclassRequirement:YouwillresetanewDatevaluebasedonthepreviousdefinitionofclassDateThethisPointerclass

Date{public:Date(int=2018,int=1,int=1);boolisEqual(Date&date);private:intday,month,year;boolcheck();};CaseStudy1-2:defineaDateclassRequirement:YoudeterminewhethertwoDateobjectsareequal.bool

Date::isEqual(Date&date){if(this->year==date.year&&this->month==date.month&&this->day==date.day)return

true;elsereturn

false;}intmain(){Dateday1(2021,9,15);Dateday2(2020,9,15);cout<<(day1.isEqual(day2)?"theyareequal":"theyareunequal")<<endl;return0;

}03StaticMembersStaticMembersDefineastudentclasswithastudentNodatamember.Youneedtodothefollowingtasks:OutputthedataofthestudentobjectsWorkoutthenumberofthestudentobjectsstudent-studentNo:int-count:int+student()+print():void+getCount():intCaseStudy2Dataabstraction:data:studentNo-intFunctionsPrint–voidprint()getCount-numberofstudentobjectsStaticMembersstudent::student()//constructor{count++;studentNo=count;}void

student::print(){cout<<

"studentNo:"

<<studentNo<<endl;}int

student::getCount(){

returncount;}intmain(){

studentst1;st1.print();cout<<st1.getCount()<<endl;

studentst2;st2.print();cout<<st2.getCount()<<endl;

studentst3;st3.print();cout<<st3.getCount()<<endl;

return0;}class

student{public:student();

voidprint();

intgetCount();private:

intcount=0;

intstudentNo=0;};Result:studentNo:11studentNo:11studentNo:11StaticMembersCountisnotdatamemberofthestudentclassintcount=0;class

student{public:student();

voidprint();

intgetCount();private:

intstudentNo=0;};student::student(){::count++;studentNo=::count;}void

student::print(){cout<<

"studentNo:"

<<studentNo<<endl;}int

student::getCount(){

return::count;}intmain(){

studentst1;st1.print();cout<<st1.getCount()<<endl;

studentst2;st2.print();cout<<st2.getCount()<<endl;

studentst3;st3.print();cout<<st3.getCount()<<endl;

return0;}studentNo:11studentNo:22studentNo:33StaticMembersclass

student{public:student();voidprint();private:intstudentNo=0;static

intcount;//thenumber};int

student::count=0;student::student(){count++;studentNo=count;}void

student::print(){cout<<"studentNo:"<<studentNo<<";count="<<count<<endl;}StaticdatamemberStaticdatamember’sinitialization:Mustbeplacedoutsidetheclass.intmain(){studentst1;st1.print();studentst2;st2.print();studentst3;st3.print();return0;}studentNo:1;count=1studentNo:2;count=2studentNo:3;count=3StaticMembersSt1StudentclassSt2St3countstudentNostudentNostudentNoStaticdatamember

isavariablethatispartofaclass,yetisnotpartofanobjectofthatclass.StaticMembersclass

student{public:student();//constructorvoidprint();private:intstudentNo=0;static

intcount;//thenumber};int

student::count=0;student::student()//constructor{count++;studentNo=count;cout<<

"count'saddress:"

<<&count<<endl;cout<<

"studentNo'saddress:"

<<&studentNo<<endl;}intmain(){

studentst1;cout<<

"st1'saddress:"

<<&st1

<<

"st1'ssize:"

<<

sizeof(st1)<<endl;studentst2;cout<<

"st2'saddress:"

<<&st2

<<

"st2'ssize:"

<<

sizeof(st2)<<endl;studentst3;cout<<

"st3'saddress:"

<<&st3

<<

"st3'ssize:"

<<

sizeof(st2)<<endl;return0;}count'saddress:0015D138studentNo'saddress:00EFFC90st1'saddress:00EFFC90st1'ssize:4count'saddress:0015D138studentNo'saddress:00EFFC84st2'saddress:00EFFC84st2'ssize:4count'saddress:0015D138studentNo'saddress:00EFFC78st3'saddress:00EFFC78st3'ssize:4StaticMemberFunctionsStaticmemberfunction

isafunctionthatneedsaccesstomembersofaclass,yetdoesnotneedtobeinvokedforaparticularobject.class

student{public:student();//constructorstatic

intgetCount();voidprint();private:intstudentNo;static

intcount;};Staticmemberfunctionint

student::count=0;student::student()//constructor{count++;studentNo=count;}void

student::print(){cout<<"studentNo:"<<studentNo<<endl;}int

student::getCount(){returncount;}StaticMember

Functionsclass

student{public:student();//constructorstatic

intgetCount();voidprint();private:intstudentNo;static

intcount;};Staticmemberfunctionint

student::count=0;student::student()//constructor{count++;studentNo=count;}void

student::print(){cout<<"studentNo:"<<studentNo<<endl;}int

student::getCount(){returncount;}intmain(){studentst1;st1.print();cout<<"studentnumberis"<<student::getCount()<<endl;studentst2;st2.print();cout<<"studentnumberis"<<student::getCount()<<endl;studentst3;st3.print();cout<<"studentnumberis"<<st3.getCount()<<endl;return0;}StaticMembersint

student::getCount(){studentNo++;//error:accesstonon-staticmember

returncount;//ok}Staticmemberfunctionsarenotattachedtoanyobject,thatis,theydonothavethispointer.Staticmemberfunctionscanonlyaccessstaticdatamembers.04FreeStoreFreeStoreLiteralconstdataStack(automaticstorage)Freestore(Heap)constantdataFunction’slocalvariables,arguments,returningdataandaddressPotentialavailablememoryGlobal(Staticdata)MemorylayoutGlobalandstaticvariablesintk1=1;intk2;static

intk3=2;static

intk4;intmain(){static

intm1=2,m2;inti=1;char*p;charstr[10]="hello";const

char*q="hello";p=(char*)malloc(100);free(p);return0;}FreeStore-dynamicmemoryAllmemoryneedsweredeterminedbeforeprogramexecutionbydefiningthevariableneeded.Buttheremaybecaseswherethememoryneedsofaprogramcanonlybedeterminedduringruntime.Whenthememoryneededdependonuserinput,

onthesecases,programsneedtodynamicallyallocateandfreememorybyusingnewanddeleteoperatorsinC++.FreeStore-dynamicmemory#include<typeinfo>intmain(){int*intp=new

int;*intp=20;int*intpt=new

int(8);cout<<typeid(intp).name()<<endl;cout<<typeid(intpt).name()<<endl;cout<<*intp<<""<<*intpt<<endl;deleteintp;deleteintpt;return0;}(malloc/freeinC)int*p=(int*)malloc(sizeof(p));AvoidmemoryleakResult:int*int*208QueriesinformationofatypeFreeStore-dynamicmemoryintmain(){intm;cout<<"Enteraninteger:";cin>>m;int*ptr=new

int[m];//dynamicone-dimensionalarrayif(ptr==NULL) cout<<"Error:memorycouldnotbeallocated";else{for(inti=0;i<m;i++)cin>>ptr[i];for(inti=0;i<m;i++)cout<<ptr[i]<<",";delete[]ptr;}int(*p)[4]=new

int[m][4];//dynamictwo-dimensionalarrayfor(inti=0;i<m;++i)for(intj=0;j<4;++j) p[i][j]=i*j;cout<<typeid(p).name()<<endl;delete[]p;return0;}FreeStoreObjectsAfreestoreobjectiscreatedusingthenewoperatoranddestroyedusingthedeleteoperator.