c++设计与编程之包含关系(包容关系)

在使用包含内容的时候，对于表示类X的对象，存在着两种主要的可选方式：
1生命一个类型为X的成员

2生命一个类型为X*或者X&的成员
如果指针值绝不改变，那么除了效率问题和写构造函数，析构函数的方式之外，这些选择方案是完全等价的：
class X{
public:
X(int);
};
class C{
X a;
X *p;
X &r;
public:
C(int i,intj,int k):a(i),p(new X(j)),r(*new X(k)){}
~C(){delete p;delete &r;}
}

1包含指针

#include<iostream>
#include<string>
using namespace std;
class Person{
public:
 Person(string name,int age){
  this->name=name;
  this->age=age;
 }
 Person(){}
 virtual void show(){
  cout<<name<<" "<<age;
 }
private:
 string name;
 int age;
};
class Student{
public:
 Student(string name,int age,string number1):p(new Person(name,age)),number(number1){}
 Student(){}
 void show(){
  p->show();
  cout<<" "<<number<<endl;
 }
private:
 string number;
 Person *p;
};
int main(){
 Student s("zhang",22,"091150");
 s.show();
 system("pause");
 return 0;
}

2包含对象

#include<iostream>
#include<string>
using namespace std;
class Person{
public:
 Person(string name,int age){
  this->name=name;
  this->age=age;
 }
 Person(){}
 virtual void show(){
  cout<<name<<" "<<age;
 }
private:
 string name;
 int age;
};
class Student{
public:
 Student(string name,int age,string number1):p(name,age),number(number1){}
 Student(){}
 void show(){
  p.show();
  cout<<" "<<number<<endl;
 }
private:
 string number;
 Person p;
};
int main(){
 
 Student s("zhang",22,"091150");
 s.show();
 system("pause");
 return 0;
}

3包含引用

#include<iostream>
#include<string>
using namespace std;
class Person{
public:
 Person(string name,int age){
  this->name=name;
  this->age=age;
 }
 Person(){}
 virtual void show(){
  cout<<name<<" "<<age;
 }
private:
 string name;
 int age;
};
class Student{
public:
 Student(string name,int age,string number1):number(number1),p(*new Person(name,age)){}
 Student():p(*new Person()){}  //这步不能少，一定得初始化
 void show(){
  p.show();
  cout<<" "<<number<<endl;
 }
 
private:
 string number;
 Person &p;
 
};
int main(){
 
 Student s("zhang",22,"091150");
 s.show();
 system("pause");
 return 0;
}

特别注意包含指针和引用指针，要new一个，最好加多一个析构函数delete删除一个，包含引用的时候，别忘了初始化。