C++面向对象程序设计双语教程（第3版）课件 class 9-operator overloading-2

ObjectivesTobeabletodefinemixedarithmeticofuser-definedtypesandbuilt-intypesTobeabletooverloadcombinatorialoperatorsTo

understandhowtoconvertobjectsfromuser-definedtypestobuilt-intypes01CombinatorialOperators03TypeConversion02MixedArithmetic04CaseStudy:Operators<<and>>01OverloadingCombinatorialOperatorsCombinatorialOperatorsForabuilt-intype,forexample,aisaninteger,ifa+=

5,itmeansa=a+5.Forexample,complexc1,c2;c2+=c1;Themeaningsofsomebuilt-inoperatorsaredefinedtobeequivalenttosomecombinationofotheroperatorsonthesameparameters.Canthecombinationaloperatorsworkontheuser-definedtypes?OverloadingCombinatorialOperatorsCaseStudy1Accordingtothetestprogram.Definethemeaningofoperator+=.intmain(){complexc1(20.3,11.3);complexc2;c2+=c1;c2.print();return0;}class

complex{public:complex(double

r=0.0,double

i=0.0):real(r),imag(i){}complexoperator+(complex&c);complex&operator=(const

complex&c);complex&operator+=(complex&c);voidprint()const;private:

doublereal,imag;};OverloadingCombinatorialOperatorscomplex

complex::operator+(complex&c){complextemp;temp.real=this->real+c.real;temp.imag=this->imag+c.imag;returntemp;}complex&complex::operator=(const

complex&c){if(this!=&c){this->real=c.real;this->imag=c.imag;}return*this;}complex&complex::operator+=(complex&c){*this=*this+c;return*this;}complex&complex::operator+=(complex&c){this->real+=c.real;this->imag+=c.imag;return*this;}02MixedArithmeticcomplexc1,c2(3.0,4.0);doubled=5.2;c2=c1+d;c2=d+c1;MixedArithmeticdouble(abuilt-intype)complex(user-definedtype)c1+dMemberfunction:c1.operator+(d)Non-memberfunction:operator+(c1,d)d+c1Memberfunction:d.operator+(c1)Non-memberfunction:operator+(d,c1)Mixedauser-definedtypes

withabuilt-intypeAnoperatorfunctioncanbedefinedforthemixedarithmeticofauser-definedtypeandbuilt-intype.MixedArithmeticAnoperatorfunctionmusteitherbememberofauser-definedtypesornon-membertakingatleastoneparameterofauser-definedtypes.Thisensuresthatausercannotchangethemeaningofanexpression.

MemberfunctionNon-memberfunctionintmain(){complexc1,c2(3.0,4.0);doubled=5.2;c2=c1+d;c2=d+c1;return0;}c2=c1.operator+(d)c2=operator+(d,c1)HowtoDefineMixedArithmeticclass

complex{public:complex(double

r=0.0,double

i=0.0):real(r),imag(i){}complex

operator+(double);friend

complex

operator+(double,complex&);private:doublereal,imag;};complex

complex::operator+(double

dd){return

complex(this->real+dd,this->imag);}complex

operator+(double

dd,complex&c){return

complex(c.real+dd,c.imag);}intmain(){complexc1,c2(3.0,4.0);doubled=5.2;c2=c1+d;c2=d+c1;return0;}03TypeConversionTypeConversioninti=5,j;doublea=3.4;j=i+a;doubleb=i/2;Forabuilt-intype,inti=5,j;doublea=3.4;j=i+(int)a;doubleb=(double)i/2;inti=5,j;doublea=3.4;j=i+static_cast<int>(a);doubleb=static_cast<double>(i)/2;C-styleC++styleUsingstatic_castoperatorinC++TypeConversionForauser-definedtypecomplexc1;doublea,b;b=c1+a;Thecompiler

cannotautomaticallyknowhowtoconvertuser-definedtypesintobuilt-intypesorbuilt-intypestouser-definedtypes.complexc1;complex

c2=

2.4;TypeConversionTherearetwowaysfortypeconversion:Fromabuilt-intypetoauser-definedtype.Fromauser-definedtypetoabuilt-intype.

Ifaclasshasaconstructorwhichcanbecalledwithasingleargument,thenthisconstructorbecomesconversionconstructorbecausesuchaconstructorallowsautomaticconversiontotheclassbeingconstructed.

Fromabuilt-intypetoauser-definedtypeTypeConversionclass

complex{public:complex(double

r,double

i):real(r),imag(i){}private:

doublereal,imag;};intmain(){complexc1(20.3,11.3);complexc2=10.5;return0;}complex::complex(double

r){real=r;imag=0.0;}complex(double);ConversionconstructorConversionConstructorsareconstructorsthatconverttypesofitsparameterintoatypeoftheclass.Thecompilerusestheseconstructorstoperformimplicitclass-typeconversions.Built-intypeUser-definedtypeTypeConversionTheconversionconstructorcannotspecify:animplicitconversionfromauser-definedtypetoabuilt-intype.Forexample,complex(classtype)int2.aconversionfromanewclasstoapreviouslydefinedclass(withoutmodifyingthedeclarationfortheoldclass).Forexample, complex(classtype)Date(classtype)TypeConversionoperatorT()constFromauser-definedtypetoabuilt-intypeSyntaxtodefineatypeconversionoperator

Atypeconversionoperatorinaclasscanconvertthe

classtypetoTtype

(built-intypesoruser-definedtypes).Itmustbedefinedasamemberfunction.TypeConversionclass

complex{public:complex(double

r,double

i):real(r),imag(i){}complex(doubler);operator

double()const;operator

int()const;voidprint()const;private:doublereal,imag;};complex::operator

double()const{returnreal;}complex::operator

int()const{return

static_cast<int>(real);}intmain(){complexc1=5.4;c1.print();doubled=(double)c1+3.4;cout<<d<<endl;intm=static_cast<int>(c1)+10;cout<<m<<endl;return0;}complex(classtype)Built-intypeTypeConversionclass

Test1{public:Test1(int

s){a=s;}

intget()const{returna;}private:

inta;};class

Test2{public:Test2(int

i):x(i){}

operator

Test1(){return

Test1(x);}

intget()const{returnx;}private:

intx;};Test2(class)->Test1(class)intmain(){

Test2t2Obj(20);cout<<

"Test2'sobject:"

<<t2Obj.get()<<endl;

Test1t1Obj_0=40;//willcompilecout<<

"Test1'sobject:"

<<t1Obj_0.get()<<endl;

Test1t1Obj_1=(Test1)t2Obj;//conversion->copycout<<

"Test1'sobject:"

<<t1Obj_1.get()<<endl;

return0;}04CaseStudy:OverloadingOperators<<and>>CaseStudy:OverloadingOperators<<and>>class

complex{public:complex(double

r=0,double

im=0):real(r),imag(im){}friend

ostre