• C++多态

• #include <iostream>
  #include <iomanip>
  using namespace std;
  
  class Base {
  public:
      virtual void f() { cout << "base" << endl; }
  };
  class Derived : public Base{
  public:
      void f() { cout << "derived" << endl; }
  };
  class Base2 {
  public:
      virtual void g() { cout << "base2 process g" << endl; } // dynamic_cast only work under polymorphic settings
  };
  class Derived2 : public Base2{
  public:
      void f() { cout << "derived2" << endl; }
  };
  
  int main() {
      /*
      Base *b = new Derived;
      b->f(); //base
  
      Base *b = new Derived;
      Derived *a = static_cast<Derived *>(b);
      a->f(); //derived
  
      Base *b = new Derived;
      b->f(); //derived, derived overwrite base in virtual table
      Derived *a = dynamic_cast<Derived *>(b);
      a->f(); //derived, same with b->f()
   */
      Base2 *b = new Derived2;
      //b->f(); // compile error
      Derived2 *a = dynamic_cast<Derived2 *>(b);
      a->f(); //derived2, same with b->f()
      return 0;
  }

• 可调用函数, 匿名函数

• auto f = [](int a, int b){return a + b;};
  cout << f(1,2) << endl; //3
  cout << [](int a, int b){return a + b;}(1,2) << endl; //3
  int a = 0; int b = 0; int c = 0;
  
  //cout << [=](int a, int b){c = 1; return a + b;}(1,2) << "\t" << c << endl;
  // error: cannot assign to a variable captured by copy in a non-mutable lambda
  //cout << [](int a, int b){int c = 1; return a + b;}(1,2) << "\t" << c << a << endl; //3 \t 0
  
  cout << [&](int a, int b){c = 1; return a + b;}(1,2) << "\t" << c << "\t" << a << endl; //3 \t 1
  cout << [&c](int a, int b){c = 1; return a + b;}(1,2) << "\t" << c << endl; //3 \t 1
  

  　　

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