C++的一些疑惑点整理及解决

equal_range:接受一个关键词，返回一个pair对组
  若关键词存在，第一个迭代器指向第一个与关键词匹配的元素，第二个指向最后一个匹配元素之后的位置
  若未找到匹配，则两个迭代器相等，都指向关键词可插入的位置。
*/

#include <iostream>
using namespace std;
class cla
{
    static int n;
    int k = 0;
public:
    cla() { n++; }
    ~cla()
    {
        n--;
        cout << "~cla" << endl;
    }
    static int get_n()
    {
        return n;
    }
};
int cla::n = 0;
int main(int argc, char const *argv[])
{
    // cla *p = new cla;
    // delete p;
    cout << "n=" << cla::get_n() << endl;
    //cout << p->Mytry() << endl;
    cout << "hhh" << endl;
    return 0;
}

Father a ;    // 基类对象
Son b ;       // 派生类对象
a = b ;       // 可以
b = a ;       // 不可以

为什么派生类对象可以给基类对象赋值呢？反之则不可以呢？这是**因为基类对象a的成员比派生类对象b的成员少。所以基类对象赋值给派生类对象时会出错**。上面是一种情况，还有另外一种情况：

Father a ;                  // 基类对象
Son b ;                     // 派生类对象
Father *pa = &b ;     // 可以
Son *pb = &a ;         // 不可以

上面的指针赋值也就是说：**基类的指针可以指向派生类对象，但是反过来则不行，派生类的指针不可以指向基类的指针**。这是为什么呢？这是因为派生类的对象所占的存储空间通常要比基类的对象大，原因就是派生类除了继承基类的成员之外，还拥有自己的成员，所以**基类的指针操作派生类的对象时，由于基类指针会向操作基类对象那样操作派生类对象，而基类对象所占用的内存空间通常小于派生类对象，所以基类指针不会超出派生类对象去操作数据。**
   **同样的道理，基类的引用可以作为派生类对象的别名，但是反过来则不行，派生类的引用不可以作为基类对象的别名**。例如：

Father a ; // 基类对象
Son b ;    // 派生类对象
Father &f = b ; // 可以
Son &s = a ;    // 不可以

#include <iostream>
#include <string>
using namespace std;
class Person
{
protected:
    string name;
    int age;
public:
    Person()
    {
    }
    Person(string s,int a)
    {
        this->name = s;
        this->age = a;
    }
public:
    virtual void show() = 0;
    virtual Person *clone() = 0;
};
class Student :public Person
{
private:
    int id;
public:
    Student()
    {
    }
    Student(string s,int a,int i):Person(s,a)
    {
        this->id = i;
    }
    void show()
    {
        cout << "name = " << name << " age = " << age << " id = " << id << endl;
    }
    Person *clone()
    {
        Student *tmp = new Student;
        *tmp = *this;
        return tmp;
    }
};
int main(int argc, char const *argv[])
{
    Person *p1 = new Student("zzz", 18, 21);
    Person *p2 = p1->clone();
    p2->show();
    return 0;
}

class Factory
{
public:
  virtual Fruit *CreateApple() = 0;
  virtual Fruit *CreateBanana() = 0;
  virtual Fruit *CreatePear() = 0;
};

class Builder
{
protected:
  House *house;
public:
  virtual void Constructor() = 0;
};
class CommonBuilder :public Builder
{
public:
  CommonBuilder(House *h)
  {
  house = h;
  }
  void Constructor()
  {
  house->SetDoor("DOOR");
  house->SetWall("WALL");
  house->SetWindow("WINDOW");
  }
};

Person *clone()
    {
        Student *tmp = new Student;
        *tmp = *this;
        return tmp;
    }

class Dir:public iFile
{
private:
    string name;
    list<iFile *> *l;
public:

class TaoBao:public Sale
{
private:
    Sale *sale;
public:
    TaoBao(Sale *s)
    {
        sale = s;
    }
    void SaleBook()
    {
        cout << "网上卖书" << endl;
        sale->SaleBook();
    }
};

class PhotoPhone:public Phone
{
private:
    Phone *phone;
public:
    PhotoPhone(Phone *p)
    {
        phone = p;
    }
    void function()
    {
        phone->function();
        cout << "相机的功能" << endl;
    }
};

class Adapter:public Current
{
private:
    Current *current;
public:
    Adapter(Current *c)
    {
        current = c;
    }
    int GetCurrent()
    {
        return 12;
    }
};

class FwFactory
{
private:
  multimap<int, Student*> *m;
public:
  FwFactory()
  {
  m = new multimap<int, Student *>;
  }
  ~FwFactory()
  {
  while (!m->empty())
  {
    Student *tmp = m->begin()->second;
    delete tmp;
    m->erase(m->begin());
  }
  delete m;
  }
  void GetPerson(int id)
  {
  string name;
  int age;
  multimap<int, Student *>::iterator it;
  it = m->find(id);
  if (it == m->end())
  {
    cout << "input the name age..." << endl;
    cin >> name >> age;
    Student *s = new Student(name, age, id);
    m->emplace(make_pair(id, s));
  }
  else
  {
    Student *s = it->second;
    cout << s->GetName() << " " << s->GetAge() << " " << s->GetId() << endl;
  }
  }
};

class Soft  //实现两种从产品的链接，把不同的产品剥离出来，耦合度低
{
protected:
  Phone *phone;
public:
  virtual void func() = 0;
};
class QQ :public Soft 
{
public:
  QQ(Phone *p)
  {
  phone = p;
  }
  void func()
  {
  phone->func();
  cout << "this is QQ" << endl;
  }
};

class Facade
{
private:
  SystemA *a;
  SystemB *b;
  SystemC *c;
public:
  Facade()
  {
  a = new SystemA;
  b = new SystemB;
  c = new SystemC;
  }
  ~Facade()
  {
  delete a;
  delete b;
  delete c;
  }
  void func()
  {
  a->func();
  b->func();
  c->func();
  }
};

class Observer  //观察者 员工
{
public:
  virtual void Subscribe(Infom *i) = 0;  //订阅
  virtual void UnSubscribe(Infom *i) = 0;  //取消订阅
  virtual void Update(string str) = 0;  //更新状态
};
class Infom  //通知者  秘书
{
public:
  virtual void Add(Observer *o) = 0;
  virtual void Remove(Observer *o) = 0;
  virtual void Notify(string str) = 0;
};
class Secretary :public Infom
{
private:
  list <Observer *> l;
public:
  void Add(Observer *o)
  {
  l.emplace_back(o);
  }
  void Remove(Observer *o)
  {
  l.remove(o);
  }
  void Notify(string str)
  {
  for (auto &it : l)
  {
    it->Update(str);
  }
  }
};