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;
}