面向对象程序设计英文教学课件：12-Templates

12Templates1OutlineFunctiontemplatesClasstemplates2KnowledgePointsWritinggenericfunctions

Book:AcceleratedC++,Chapter83ReferenceMaterialsTemplates

Book:C++HowtoProgram(8thedition),Chapter14(15pages)IntroductionManyoftheideasandexamplespresentedinthelastfewlessonshaveillustratedwaysofmakingcode"generalpurpose".SuchasoverloadingfunctionandinheritanceTheideaofatemplateisthatitdefinesoperationsforanunboundedvarietyofrelateddatatypes.ProgrammingusingtypesasparametersIntroductionKindsoftemplateFunctiontemplatesClasstemplatesTheydescribe,insomegeneralway,howtomanipulatedataelements.Theyworkwithanykindofdatathatsupportstherequiredoperations.TothinkAfunctionmax()takestwodataelementsasarguments,andreturnsthelarger.Wmax(inta,intb){

if(a>b)

returna;

else

returnb;}doublemax(doublea,doubleb){

if(a>b)

returna;

else

returnb;}Boxmax(Boxa,Box

b){

if(a>b)

returna;

else

returnb;}Therehastobeabetterway!template<typenameT>Tmax(constT&a,constT&b){

if(a>b)

returna;

else

returnb;}IndicatesatemplateisbeingdefinedTisaformaltemplatetypeparameterFunctiontemplateDescribesafunctionformatthatwheninstantiatedwithparticularsgeneratesafunctiondefinitionWriteonce,usemultipletimesFunctionTemplatesCodesegmentintInput1=PromptAndRead();intInput2=PromptAndRead();cout<<max(Input1,Input2)<<endl;Causesthefollowingfunctiontobegeneratedfromourtemplateintmax(const

int&a,const

int&b){

if(a>b)

returna;

else

returnb;}TemplateFunctionCodesegmentdoubleValue1=4.30;doubleValue2=19.54;cout<<max(Value1,Value2)<<endl;Causesthefollowingfunctiontobegeneratedfromourtemplatedoublemax(const

double&a,const

double&b){

if(a>b)

returna;

else

returnb;}TemplateFunctionOperator>needstobedefinedfortheactualtemplateparametertype.If>isnotdefined,thenacompile-timeerroroccursCodesegmentBoxb1(6,4,7);Boxb2(5,5,8);cout<<max(b1,b2)<<endl;CausesthefollowingfunctiontobegeneratedfromourtemplateBoxmax(constBox&a,constBox&b)

{

if(a>b)

returna;

else

returnb;}TemplateFunctionNotemplatefunction,justacompile-timeerror

Thetemplateparametersmustbeexactmachwheninstantiatingafunctiontemplate.CodesegmentBoxb1(6,4,7);doubled=2.0;cout<<max(b1,d)<<endl;Whatfunctionwillbegeneratedfromourtemplate???TemplateFunctiontemplate<typenameT>TMin(constT&a,constT&b){

if(a<b)

returna;

else

returnb;}intMin(const

int&a,const

int&b){

if(a<b)

returna;

else

returnb;}intmain(){

inta=1,b=2;cout<<Min(a,b)<<endl;

return0;}Forfollowingcodesegment,whatishappened?Compilermatchoverloadingfunctionfirst,andthenmatchtemplatefunctionFunctionTemplatesAdviceboolfind(intval);boolfind(constMatrix&val);template<typenameelemType>boolfind(elemType&val);

Indefinitionoftemplate,theparametersoffunctioncommonlyusereference.ClassTemplatedeclarationtemplate<template_arguments_list>classclass_name{//definitionoftemplate};template<template_arguments_list>return_typeclass_name<template_argument_names_list>::member_function_name(member_function_argument_list){ //body_of_member_function}template<typenameT,intn>classTC{public:TC();

voidAssign(Tsrc);

//...private:TValueArray[n];}ThevaluetemplateparameterThetypetemplateparameterClassTemplatesTC<char,80>A;TC<int,125>B;classTC{public:TC();

voidAssign(charsrc);

//...private:

charValueArray[80];};TCA;classTC{public:TC();

voidAssign(intsrc);

//...private:

intValueArray[125];};TCB;ClassTemplatesExample:generaldatastoringclasstemplate<typenameT>classStore //Classtemplate:implementstoringanytypedata{private: Titem; //tostoredata boolhaveValue; //tomarkwhetherthedataisexistedpublic: Store(void); //defaultconstructor TgetElem(void); //togetthedata voidputElem(Tx); //tostorethedata};//implementationofthedefaultconstructortemplate<typenameT>Store<T>::Store(void):haveValue(0){}template<typenameT>//implementationofthegetElem()TStore<T>::getElem(void){ if(!haveValue) //ifnodatainstore,exittheprogram {cout<<"Noitempresent!"<<endl;exit(1); } returnitem;//returnthestoreddata}template<typenameT>//implementationoftheputElem()voidStore<T>::putElem(Tx){ haveValue=true; item=x;}structStudent{ intid;//学号

floatgpa;//平均分};intmain(){ Studentg={1000,23}; Store<int>s1,s2; Store<Student>s3; s1.putElem(3); s2.putElem(-7); cout<<s1.ge