第5章堆与拷贝构造函数-PPT幻灯片

第5章堆与拷贝构造函数

5.1关于堆C++的内存格局通常分为四个区：代码区、全局数据、栈区、堆区。全局变量、静态数据、常量存放在全局数据区，所有类成员函数和非成员函数代码存放在代码区，为运行函数而分配的局部变量、函数参数、返回地址等存放在栈区，余下的空间都被作为堆区。

第五章堆与拷贝构造函数5.2需要new和delete的原因

使用new和delete比malloc()和free()简单，不用头文件声明。从程序设计的需要来看，在分配内存申请的时候，总是知道分配的空间派什么用，而且分配空间大小总是某个数据类型（包括类类型）的整数倍。类对象的建立是分配空间、构造结构以及初始化的三位一体，它们统一由构造函数来完成。malloc()函数在分配空间的时候不能调用构造函数。第五章堆与拷贝构造函数5.3分配堆对象如果是分配局部对象，则在该局部对象退出作用域时自动调用析构函数。但是堆对象的生命期是整个程序生命期，所以除非程序运行完毕，否则堆对象生命不会到期。堆对象析构是在释放堆对象语句delete之时。

构造函数可以有参数，所以跟在new的类型后也可以有参数。从堆上分配对象数组，只能调用默认的构造函数，不能调用其它任何构造函数。voidfn(){TDate*pS;pS=newTDate;……deletepS;}第五章堆与拷贝构造函数#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;};第五章堆与拷贝构造函数#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第五章堆与拷贝构造函数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";}第五章堆与拷贝构造函数ConstructingnewstudentRandyCallingfn()ConstructingcopyofRandyInfunctionfn()DestructingcopyofRandyReturnedfromfn()DestructingRandy第五章堆与拷贝构造函数5.5默认拷贝构造函数类定义中，如果未提供自己的拷贝构造函数，则C++提供一个默认拷贝构造函数，就像没有提供构造函数时，C++提供默认构造函数一样。C++提供的默认拷贝构造函数的功能是把初始值对象的每个数据成员的值都复制到新建立的对象中，即完成一个成员一个成员的拷贝。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];};第五章堆与拷贝构造函数classTutor{public:Tutor(Student&s):student(s){cout<<"Constructingtutor\n";}protected:Studentstudent;};voidfn(Tutortutor){cout<<"Infunctionfn()\n";}voidmain(){Studentrandy("Randy");Tutortutor(randy);cout<<"Callingfn()\n";fn(tutor);cout<<"Returnedfromfn()\n";}第五章堆与拷贝构造函数voidfn(Tutortutor){cout<<"Infunctionfn()\n";}voidmain(){Studentrandy("Randy");Tutortutor(randy);cout<<"Callingfn()\n";fn(tutor);cout<<"Returnedfromfn()\n";}第五章堆与拷贝构造函数ConstructingnewstudentRandyConstructingcopyofRandyConstructingtutorCallingfn()ConstructingcopyofcopyofRandyInfunctionfn()DestructingcopyofcopyofRandyReturnedfromfn()DestructingcopyofRandyDestructingRandy第五章堆与拷贝构造函数

5.6深拷贝构造函数、默认拷贝构造函数和赋值都将现存的一个对象的值拷贝到一个新的存储位置，浅拷贝正是这种拷贝，它只拷贝一个对象数据成员的值，但不拷贝资源的分配。浅拷贝也称为逐成员拷贝。深拷贝是在浅拷贝的基础上，重复拷贝被拷贝者引用的资源。凡是需要析构函数深拷贝的时候，也需要深拷贝。S对象T对象资源classPerson{public:Person(char*pN){cout<<"Constructing"<<pN<<endl;pName=newchar[strlen(pN)+1];if(pName!=0)strcpy(pName,pN);}~Person(){cout<<"Destructing"<<pName<<endl;pName[0]='\0';deletepName;}protected:char*pName;};voidmain(){Personp1("Randy");Personp2=p1;//即Personp2(p1);}第五章堆与拷贝构造函数ConstructingRandyDestructingRandyDestructingNullpointerassignment第五章堆与拷贝构造函数

5.7临时对象Studentfn(){//……Studentms(“Randy”);Return(ms);}voidmain(){Students;s=fn();//……}voidmain(){Student&s=fn();//……}很危险!第五章堆与拷贝构造函数5.8无名对象直接调用构造函数可以产生无名对象voidmain(){Student&refs=Student(“Randy”);Students=Student(“Jenny”);fn(Student(“Danny”));//……}第五章堆与拷贝构造函数

5.9类型转换classStudent{public:Student(char*);//……};voidfn(Student&s);voidmain(){fn(“Jenny”);}第五章堆与拷贝构造函数classexample

{public:

intnum;

public:

~example(){cout<<"Destroying"<<num<<endl;};

example(intn){num=n;cout<<"Initialing"<<num<<endl;};

voidprint(){cout<<num<<endl;};

};

voidmain()

{exampleX(0