实验目的和要求
1、熟悉类的定义格式和类中成员的访问权限。
2、构造函数与析构函数的调用时机与顺序。
3、掌握对象的定义以及对象的初始化的时机与方法。
实验内容
1、下面程序sy3_1.cpp中用ERROR标明的语句有错吧,在不删除和增加代码行的情况下,改正错误语句,使其正确运行。
运行程序如下:
#include<iostream> using namespace std; class Aa { public: Aa(int i=0){a=i;cout<<"Constructor"<<a<<endl;} ~Aa(){cout<<"Destructor"<<a<<endl;} void print(){cout<<a<<endl;} private: int a; }; int main() { Aa a1(1),a2(2); a1.print(); cout<<a2.a<<endl;//ERROR return 0; }
错误提示:
修改如下:
#include<iostream> using namespace std; class Aa { public: Aa(int i=0){a=i;cout<<"Constructor"<<a<<endl;} ~Aa(){cout<<"Destructor"<<a<<endl;} void print(){cout<<a<<endl;} private: int a; }; int main() { Aa a1(1),a2(2); a1.print(); a2.print(); return 0; }
运行结果:
2、调试下列程序:
#include<iostream> using namespace std; class TPoint { public: TPoint(int x=0,int y=0){X=x,Y=y;} TPoint(TPoint &p); ~TPoint(){cout<<"Destructor is called\n";} int getx(){return X;} int gety(){return Y;} private: int X,Y; }; TPoint::TPoint(TPoint &p) { X=p.X; Y=p.Y; cout<<"Copy-initialization Constructor is called\n"; } int main() { TPoint p1(4,9); TPoint p2(p1); TPoint p3=p2; TPoint p4,p5(2); cout<<"p3=("<<p3.getx()<<","<<p3.gety()<<")\n"; return 0; }
在程序中,将TPoint类的带有两个参数的构造函数进行修改,在函数体内增添下述语句:
cout<<"Constructor is called\n";
(1)写出程序的输出结果,并解释输出结果;
#include<iostream> using namespace std; class TPoint { public: TPoint(int x=0,int y=0){X=x,Y=y;} TPoint(TPoint &p); ~TPoint(){cout<<"Destructor is called\n";} int getx(){return X;} int gety(){return Y;} private: int X,Y; }; TPoint::TPoint(TPoint &p) { X=p.X; Y=p.Y; cout<<"Copy-initialization Constructor is called\n"; } int main() { TPoint p1(4,9); TPoint p2(p1); TPoint p3=p2; TPoint p4,p5(2); cout<<"p3=("<<p3.getx()<<","<<p3.gety()<<")\n"; return 0; }
在程序中,将TPoint类的带有两个参数的构造函数进行修改,在函数体内增添下述语句:
cout<<"Constructor is called\n";
(1)写出程序的输出结果,并解释输出结果;
#include<iostream> using namespace std; class TPoint { public: TPoint(int x=0,int y=0){X=x,Y=y;} TPoint(TPoint &p); ~TPoint(){cout<<"Destructor is called\n";} int getx(){return X;} int gety(){return Y;} private: int X,Y; }; TPoint::TPoint(TPoint &p) { X=p.X; Y=p.Y; cout<<"Constructor is called\n"; cout<<"Copy-initialization Constructor is called\n"; } int main() { TPoint p1(4,9); TPoint p2(p1); TPoint p3=p2; TPoint p4,p5(2); cout<<"p3=("<<p3.getx()<<","<<p3.gety()<<")\n"; return 0; }
运行结果如下:
(2)按下列要求进行调试:
在主函数体内,添加下列说明语句:
TPoint p4,p5(2);
调试程序会出现什么现象?为什么?如何解决?(提示:对已有的构造函数进行适当修改)结合运行结果分析如何使用不同的构造函数创建不同的对象。
现象:
为什么:
如何解决:
3、对教材中Li3_11.cpp的主函数做如下修改:
(1)将Heapclass *pa1,*pa2 改为Heapclass *pa1,*pa2,*pa3;
(2)在语句pa2=new Heapclass 后增加语句pa3=new Heapclass(5);
(3)将语句 if(!pa1||!pa2) 改为if(!pa1||!pa2||!pa3)
(4)在语句delete pa2 后增加语句delete pa3;
写出程序的输出结果,并解释输出结果。
程序如下:
#include<iostream> using namespace std; class Heapclass { public: Heapclass(int x); Heapclass(); ~Heapclass(); private: int i; }; Heapclass::Heapclass(int x) { i=x; cout<<"Contstructor is called. "<<i<<endl; } Heapclass::Heapclass() { cout<<"Default Contstructor is called."<<endl; } Heapclass::~Heapclass() { cout<<"Default is called."<<endl; } int main() { Heapclass *pa1,*pa2,*pa3; pa1=new Heapclass(4); pa2=new Heapclass; pa3=new Heapclass(5); if(!pa1||!pa2||!pa3) { cout<<"Out of Mcmory!"<<endl; return 0; } cout<<"Exit main"<<endl; delete pa1; delete pa2; delete pa3; return 0; }
运行结果如下:
解释: