[置顶] 运算符重载,浅拷贝(logical copy) ,vs, 深拷贝(physical copy)，三大件（bigthree problem）

一般的我们喜欢这样对对象赋值：

Person p1;Person p2=p1;

classT object(another_object), or A a(b);

classT object = another object;

class A

{

// …

};

int main( )

{

A x;

A y(x);

// …

A z = x;

z = y;

}

这样的话，如果成员变量中有指针的话，就容易造成指针的二次删除。这样就需要我们显示的在类中实现

1、拷贝构造，

2、赋值运算符重载。

1）、判断是不是自赋值，2）、释放旧空间，3）、开辟新空间。4）、内容本身的 拷贝，5）、返回*this

3、析构函数（释放指针指向的空间）。

这三步使类实现深拷贝，从而避免浅拷贝的二次删除问题。俗称三大件。

class Vector

{

private:

int *rep;

int size;

void clone(const Vector& a);

void dispose( );

public:

Vector(int s=0);

// a default constructor initializing all members of rep to 0 if s is not 0.

Vector( int*, int );

// a constructor creates a Vector object from an ordinary array

Vector(const Vector& v); // a copy constructor

~Vector( ) {dispose( );} // a destructor

int get_size( ) const {return size;} // an accessor

const Vector& operator=(const Vector& x);

int& operator[ ](int index) {return rep[index];}

const int& operator[ ](int index) const {return rep[index];}

};

//Vector v;

//V = a;

//Vector v(a);

void Vector::clone(const Vector& a)

{

this->size = a.size; rep = new int[size];

for (int count = 0; count < size; ++count)

rep[count] = a[count]; // (*this)[count] = a[count];

// rep[count] = a.rep[count];

}

void Vector::dispose( )

{

delete [ ] rep;

rep = NULL;

}

Vector::Vector(int s) : size(s)

{

if (size <= 0)

{ rep = NULL; }

else

{

rep = new int[size];

for (int count = 0; count < size; ++count)

{ rep[count] = 0; } }

}

Vector::Vector(int* a, int s) : size(s), rep(new int[s])

{

for (int count = 0; count < size; ++count)

{ rep[count] = a[count]; }

}

Vector::Vector(const Vector& v)

{ clone(v); }

//for example: Vector a, v; a.=(v);

const Vector& Vector::operator=(const Vector& x)

{

if ( this != &x ) //Vector v; Vector* p = &v; v = *p;

{

delete []rep;

this->size = x.size;

rep = new int[size];

for (int count = 0; count < size; ++count)

rep[count] = x[count];

}

return *this;

}

// overloading operator <<, not a friend function

ostream& operator<<(ostream& out, const Vector& x)

{

int s = x.get_size( );

for (int i = 0; i < s; ++i)

{

out << x[i]<<endl; // out<<x.rep[i]<<endl;

}

out << endl;

return out;

}

bool operator==(const Vector& a, const Vector& b)

{

bool yes = true;

if (a.get_size( ) != b.get_size( ))

{ yes = false; }

else

{

int s, index = 0;

s = a.get_size( );

while (index < s && a[index] == b[index])

{ ++index; }

if (index < s)

{ yes = false; }

}

return yes;

}

int main()

{

Vecter vec1;

cout<<vec1<<endl;

int array[5] = {1,2,3,4,5};

Vector vec2( array, 5 );

cout<<vec2<<endl;

Vector vec3( vec2 );

cout<<vec3<<end;

if( vec3 == vec2 )

{

Cout<<”The vector3 is equal to vector2”<<endl;

}

Vector vec4;

vec4 = vec3;

cout<<vec4<<end;

return 0;

}

1. 实现一个字符串类String，功能包括： 1、Big Three 2、下标操作符重载 3、输入输出操作符重载 4、==操作符重载 5、+操作符重载

#include <iostream>
using namespace std;
class String
{
public:
String(char* c=""):len(strlen(c))
{
if(!c)
{
str=new char[1];
strcpy(str,"");
}
else
{
str=new char[strlen(c)+1];
strcpy(str,c);
}
}
String(const String& s)
{
len=s.len;
if(!s.str)
{
str=new char[1];
strcpy(str,"");
}
else
{
str=new char[len+1];
strcpy(str,s.str);
}
}
~String()
{
if(str)
{
delete []str;
str=NULL;
}
}
const String& operator=(const String& s)
{
if(this!=&s)
{
len=s.len;
delete str;
if(!s.str)
{
str=new char[1];
strcpy(str,"");
}
else
{
str=new char[len+1];
strcpy(str,s.str);
}
}
return *this;
}
const char& operator[](int index)const
{
return str[index];
}
char& operator[](int index)
{
return str[index];
}

bool operator==(const String& s)
{
if(len!=s.len)
return false;
while (len--)
{
if((*this)[len]!=s[len])
return false;
}
return true;
}
const String operator+(const String& s)
{
char* p=new char[len+s.len+1];
strcpy(p,str);
strcat(p,s.str);
String newStr(p);
return newStr;
}
friend ostream& operator<<(ostream& out,const String & s);
friend istream& operator>>(istream& in, String & s);
private:
int len;
char* str;
};
ostream& operator<<(ostream& out,const String & s)
{
out<<s.str<<"  "<<s.len<<endl;
return out;
}
istream& operator>>(istream& in,String & s)
{
cout<<"请输入小于100的字符串"<<endl;
delete s.str;
s.str=new char[100];
in>>s.str;
s.len=strlen(s.str);
return in;
}
int main()
{
String s1,s2;
cin>>s1;
cin>>s2;
cout<<(s1==s2)<<endl;
cout<<"s1+s2"<<endl;
cout<<(s1+s2)<<endl;
s1=s2;
cout<<s1<<" s2= "<<s2;
cout<<(s1==s2)<<endl;
return 0;
}

. 写一个学生类，从person类继承，增加的属性为成绩f和评语label（字符串）。

person: name,age,print(),要求使用三大件，输出重载，==重载，下标重载。

#include<iostream>
#include<string.h>
using namespace std;
class Person
{
friend ostream& operator<<(ostream& out,Person& p);
public:
Person(int a ,char * c):age(a)
{
if(!c)
{
name=NULL;
}
else
{
name=new char[strlen(c)+1];
strcpy(name,c);
}
}
Person(Person& p)
{
if(!p.name)
{
name=NULL;
}
else
{
name=new char[strlen(p.name)+1];
strcpy(name,p.name);
}
}
~Person()
{
if(name!=NULL)
delete []name;
}
const Person& operator=(Person& p)
{
if(this!=&p)
{
delete[]name;
name=new char[strlen(p.name)+1];
strcpy(name,p.name);
}
return *this;
}
void print()
{
cout<<*this;
}
protected:
int age;
char* name;

};
ostream& operator<<(ostream& out,Person& p)
{
out<<"姓名："<<p.name<<"  年龄:"<<p.age<<endl;
return out;
}
class Student:public Person
{
friend ostream& operator<<(ostream& out,Student& s);
public:
Student(int a,char* n,float fl=0,char* c=""):Person(a,n),f(fl)
{
if(!c)
{
lable=NULL;
}
else
{
lable=new char[strlen(c)+1];
strcpy(lable,c);
}
}
Student(Student& s):Person(s)
{
if(!s.lable)
{
f=s.f;
lable=NULL;
lable=new char[strlen(s.lable)+1];
strcpy(lable,s.lable);
}
}
~Student()
{
if(lable!=NULL)
delete[] lable;
}
const Student& operator=(Student& s)
{
if(this!=&s)
{
Person::operator=(s);
if(!s.lable)
{
f=s.f;
lable=NULL;
}
else
{
f=s.f;
delete[]lable;
lable=new char[strlen(s.lable)+1];
strcpy(lable,s.lable);
}
}
}
void print()
{
cout<<*this;
}
private:
float f;
char* lable;
};
ostream& operator<<(ostream& out,Student& s)
{
out<<"姓名："<<s.name<<"  年龄:"<<s.age<<endl;
out<<"成绩："<<s.f<<"  评语:"<<s.lable<<endl;
return out;
}
int main()
{
Person *p=new Person(18,"小方");
p->print();

Student* s=new Student(18,"小芳",99,"山上有个姑娘叫小芳");
s->print();
Person* p2=s;
p2->print();
((Student*)p2)->print();
(*((Student*)p2)).print();

Student s1(99,"阿黄",99,"上有个姑娘叫阿黄");
Person& p3=s1;
p3.print();
s1.print();
((Student&)p3).print();
return 0;
}

1.
Person为基类：虚函数为 dailywork() ~Person()

定义三个子类：Student Doctor(char* label) Driver(char* label)

主函数：定义基类指针数组，动态创建子类对象，调用成员函数，删除创建的对象

#include<iostream.h>

#include<string.h>

class Person

{

friend ostream& operator<<(ostream& out,Person& p);

public:

Person(int a =0,char * c=""):age(a)

{

if(!c)

{

name=NULL;

}

else

{

name=new char[strlen(c)+1];

strcpy(name,c);

}

}

Person(const Person& p)

{

if(!p.name)

{

name=NULL;

}

else

{

name=new char[strlen(p.name)+1];

strcpy(name,p.name);

}

}

virtual~Person()

{

if(name!=NULL)

delete []name;

}

virtual void dailywork()

{

cout<<"<^.^> 吃饭 劳动 睡觉 活下去 <^.^>";

}

const Person& operator=(const Person& p)

{

if(this!=&p)

{

delete[]name;

name=new char[strlen(p.name)+1];

strcpy(name,p.name);

}

return *this;

}

void print()

{

cout<<*this;

}

protected:

int age;

char* name;

};

ostream& operator<<(ostream& out,Person& p)

{

out<<"姓名："<<p.name<<" 年龄:"<<p.age<<endl;

return out;

}

class Student:public Person

{

friend ostream& operator<<(ostream& out,Student& s);

public:

Student(int a,char* n,float fl=0,char* c=""):Person(a,n),f(fl)

{

if(!c)

{

lable=NULL;

}

else

{

lable=new char[strlen(c)+1];

strcpy(lable,c);

}

}

Student(Student& s):Person(s)

{

if(!s.lable)

{

f=s.f;

lable=NULL;

lable=new char[strlen(s.lable)+1];

strcpy(lable,s.lable);

}

}

~Student()

{

if(lable!=NULL)

delete[] lable;

}

void dailywork()

{

Person::dailywork();

cout<<"<^.^> 学习 学习 再学习 <^.^>"<<endl;

}

const Student& operator=(const Student& s)

{

if(this!=&s)

{

Person::operator=(s);

if(!s.lable)

{

f=s.f;

lable=NULL;

}

else

{

f=s.f;

delete[]lable;

lable=new char[strlen(s.lable)+1];

strcpy(lable,s.lable);

}

}

}

void print()

{

cout<<*this;

}

private:

float f;

char* lable;

};

ostream& operator<<(ostream& out,Student& s)

{

out<<"姓名："<<s.name<<" 年龄:"<<s.age<<endl;

out<<"成绩："<<s.f<<" 评语:"<<s.lable<<endl;

return out;

}

class Doctor:public Person

{

public:

Doctor(int _age,char *_name,char* _lable):Person(_age,_name)

{

if(!_lable)

{

lable=new char[1];

strcpy(lable,"");

}

else

{

lable=new char[strlen(_lable)+1];

strcpy(lable,_lable);

}

}

Doctor(const Doctor& d):Person(d)

{

if(!d.lable)

{

lable=NULL;

}

else

{

lable=new char[strlen(d.lable)+1];

strcpy(lable,d.lable);

}

}

~Doctor()

{

if(lable)

{

delete []lable;

lable=NULL;

}

}

const Doctor& operator=(const Doctor& d)

{

if(this!=&d)

{

Person::operator=(d);

if(!d.lable)

{

lable=NULL;

}

else

{

lable=new char[strlen(d.lable)+1];

strcpy(lable,d.lable);

}

}

return *this;

}

void dailywork()

{

Person::dailywork();

cout<<"<^.^> 救死 扶伤 治病 抓药 <^.^>"<<endl;

}

private:

char* lable;

friend const ostream& operator<<(ostream& out,const Doctor & d);

};

const ostream& operator<<(ostream& out,const Doctor& d)

{

out<<(Person&)d<<endl;

out<<d.lable<<endl;

return out;

}

class Driver:public Person

{

public:

Driver(int _age,char *_name,char* _lable):Person(_age,_name)

{

if(!_lable)

{

lable=new char[1];

strcpy(lable,"");

}

else

{

lable=new char[strlen(_lable)+1];

strcpy(lable,_lable);

}

}

Driver(const Driver& d):Person(d)

{

if(!d.lable)

{

lable=NULL;

}

else

{

lable=new char[strlen(d.lable)+1];

strcpy(lable,d.lable);

}

}

~Driver()

{

if(lable)

{

delete []lable;

lable=NULL;

}

}

const Driver& operator=(const Driver& d)

{

if(this!=&d)

{

Person::operator=(d);

if(!d.lable)

{

lable=NULL;

}

else

{

lable=new char[strlen(d.lable)+1];

strcpy(lable,d.lable);

}

}

return *this;

}

void dailywork()

{

Person::dailywork();

cout<<"<^.^> 驾驶 开车 拉货 跑四方 <^.^>"<<endl;

}

private:

char* lable;

friend const ostream& operator<<(ostream& out,const Driver & d);

};

const ostream& operator<<(ostream& out,const Driver & d)

{

out<<(Person&)d<<endl;

out<<d.lable<<endl;

return out;

}

int main()

{

Person *p=new Person(18,"小方");

p->print();

Student* s=new Student(18,"小芳",99,"山上有个姑娘叫小芳");

s->print();

Person* p2=s;

p2->print();

((Student*)p2)->print();

(*((Student*)p2)).print();

Student s1(99,"阿黄",99,"上有个姑娘叫阿黄");

Person& p3=s1;

p3.print();

s1.print();

((Student&)p3).print();

cout<<"====//开始====="<<endl;

Person array[3]={Person(30,"张二狗"),Person(18,"二凤"),Person(18,"Mis Y")};

Person *parray[3];

parray[0]=array;

parray[1]=array+1;

parray[2]=array+2;

parray[0]->dailywork();

array[0].dailywork();

cout<<"========="<<endl;

parray[0]=new Student(20,"张三",99,"好学生");

parray[1]=new Driver(22,"李四","好司机");

parray[2]=new Doctor(30,"王五","好大夫");

for(int i=0;i<3;i++)

{

parray[i]->dailywork();

delete []parray[i];

}

//Student sarry();

//Student** sParry=new Student *[2];

//delete []sParry;

return 0;

}