第5章堆與拷貝構(gòu)造函數(shù)

面向?qū)ο蟪绦蛟O(shè)計(jì)（C++）OrientedObjectProgramming(C++)主講：嚴(yán)冬梅第5章堆與拷貝構(gòu)造函數(shù)第5章堆與拷貝構(gòu)造函數(shù)

5.1關(guān)于堆C++的內(nèi)存格局通常分為四個(gè)區(qū)：代碼區(qū)、全局?jǐn)?shù)據(jù)、棧區(qū)、堆區(qū)。全局變量、靜態(tài)數(shù)據(jù)、常量存放在全局?jǐn)?shù)據(jù)區(qū)，所有類成員函數(shù)和非成員函數(shù)代碼存放在代碼區(qū)，為運(yùn)行函數(shù)而分配的局部變量、函數(shù)參數(shù)、返回地址等存放在棧區(qū)，余下的空間都被作為堆區(qū)。

第五章堆與拷貝構(gòu)造函數(shù)5.2需要new和delete的原因

使用new和delete比malloc()和free()簡(jiǎn)單，不用頭文件聲明。從程序設(shè)計(jì)的需要來(lái)看，在分配內(nèi)存申請(qǐng)的時(shí)候，總是知道分配的空間派什么用，而且分配空間大小總是某個(gè)數(shù)據(jù)類型（包括類類型）的整數(shù)倍。類對(duì)象的建立是分配空間、構(gòu)造結(jié)構(gòu)以及初始化的三位一體，它們統(tǒng)一由構(gòu)造函數(shù)來(lái)完成。malloc()函數(shù)在分配空間的時(shí)候不能調(diào)用構(gòu)造函數(shù)。第五章堆與拷貝構(gòu)造函數(shù)5.3分配堆對(duì)象如果是分配局部對(duì)象，則在該局部對(duì)象退出作用域時(shí)自動(dòng)調(diào)用析構(gòu)函數(shù)。但是堆對(duì)象的生命期是整個(gè)程序生命期，所以除非程序運(yùn)行完畢，否則堆對(duì)象生命不會(huì)到期。堆對(duì)象析構(gòu)是在釋放堆對(duì)象語(yǔ)句delete之時(shí)。

構(gòu)造函數(shù)可以有參數(shù)，所以跟在new的類型后也可以有參數(shù)。從堆上分配對(duì)象數(shù)組，只能調(diào)用默認(rèn)的構(gòu)造函數(shù)，不能調(diào)用其它任何構(gòu)造函數(shù)。voidfn(){TDate*pS;pS=newTDate;……deletepS;}第五章堆與拷貝構(gòu)造函數(shù)5.4拷貝構(gòu)造函數(shù)需要性對(duì)象初始化

Tdated1(1999,9,9);

Tdated2=d1;函數(shù)參數(shù)傳遞

voidfn(Tdated){}

fn(d1);函數(shù)的返回值是類對(duì)象Tdatefn(){}

Tdated=fn();拷貝構(gòu)造函數(shù)實(shí)際上也是構(gòu)造函數(shù)，其功能是用一個(gè)已知的對(duì)象來(lái)初始化一個(gè)被創(chuàng)建的同類的對(duì)象。第五章堆與拷貝構(gòu)造函數(shù)格式

class類名{public:類名(形參表);構(gòu)造函數(shù)類名(類名&);//拷貝構(gòu)造函數(shù)聲明};類名::類名(類名&對(duì)象名)//拷貝構(gòu)造函數(shù)定義{函數(shù)體}Tdate::Tdate(Tdate&d){}拷貝構(gòu)造函數(shù)是特殊的構(gòu)造函數(shù)，形參是本類對(duì)象的引用，其作用是使用一個(gè)已經(jīng)存在的對(duì)象去初始化一個(gè)新的同類的對(duì)象。第五章堆與拷貝構(gòu)造函數(shù)#include<iostream.h>classTPoint{public:TPoint(intx,inty){X=x;Y=y;cout<<"ConstructorCalled."<<X<<","<<Y<<"\n";}TPoint(TPoint&p){X=p.X;Y=p.Y;cout<<"CopyconstructorCalled."<<X<<","<<Y<<"\n";}~TPoint(){cout<<"DestructorCalled."<<X<<","<<Y<<"\n";}intXcoord(){returnX;}intYcoord(){returnY;}private:intX,Y;};第五章堆與拷貝構(gòu)造函數(shù)#include<iostream.h>#include“point.h”voidmain(){TPointp1(5,7);TPointp2(p1);cout<<“p2=(“<<p2.Xcoord()<<“,”<<p2.Ycoord()<<“)”<<endl;

}ConstructorCalled.5,7CopyconstructorCalled.5,7p2=(5,7)DestructorCalled.5,7DestructorCalled.5,7第五章堆與拷貝構(gòu)造函數(shù)TPointf(TPointq){cout<<"Infunctionf!\n";intx,y;x=q.Xcoord()+10;y=q.Ycoord()+20;TPointr(x,y);returnr;}voidmain(){TPointm(20,35),p(0,0);TPointn(m);p=f(n);cout<<"Return,inmain().\n";cout<<"p=("<<p.Xcoord()<<","<<p.Ycoord()<<")"<<endl;}ConstructorCalled.20,35ConstructorCalled.0,0CopyconstructorCalled.20,35CopyconstructorCalled.20,35Infunctionf!ConstructorCalled.30,55CopyconstructorCalled.30,55DestructorCalled.30,55DestructorCalled.20,35DestructorCalled.30,55Return,inmain().p=(30,55)DestructorCalled.20,35DestructorCalled.30,55DestructorCalled.20,35classStudent{public:Student(char*pName="noname",intssId=0){strncpy(name,pName,40);name[39]='\0';id=ssId;cout<<"Constructingnewstudent"<<pName<<endl;}Student(Student&s){cout<<"Constructingcopyof"<<<<endl;strcpy(name,"copyof");strcat(name,);id=s.id;}~Student(){cout<<"Destructing"<<name<<endl;}protected:charname[40];intid;};voidfn(Students){cout<<"Infunctionfn()\n";}voidmain(){Studentrandy("Randy",1234);cout<<"Callingfn()\n";fn(randy);cout<<"Returnedfromfn()\n";}第五章堆與拷貝構(gòu)造函數(shù)ConstructingnewstudentRandyCallingfn()ConstructingcopyofRandyInfunctionfn()DestructingcopyofRandyReturnedfromfn()DestructingRandy第五章堆與拷貝構(gòu)造函數(shù)5.5默認(rèn)拷貝構(gòu)造函數(shù)類定義中，如果未提供自己的拷貝構(gòu)造函數(shù)，則C++提供一個(gè)默認(rèn)拷貝構(gòu)造函數(shù)，就像沒(méi)有提供構(gòu)造函數(shù)時(shí)，C++提供默認(rèn)構(gòu)造函數(shù)一樣。C++提供的默認(rèn)拷貝構(gòu)造函數(shù)的功能是把初始值對(duì)象的每個(gè)數(shù)據(jù)成員的值都復(fù)制到新建立的對(duì)象中，即完成一個(gè)成員一個(gè)成員的拷貝。classStudent{public:Student(char*pName="noname"){cout<<"Constructingnewstudent"<<pName<<endl;strncpy(name,pName,sizeof(name));name[sizeof(name)-1]='\0';}Student(Student&s){cout<<"Constructingcopyof"<<<<endl;strcpy(name,"copyof");strcat(name,);}~Student(){cout<<"Destructing"<<name<<endl;}protected:charname[40];};第五章堆與拷貝構(gòu)造函數(shù)classTutor{public:Tutor(Student&s):student(s){cout<<"Constructingtutor\n";}protected:Studentstudent;