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  1. #include <iostream>
  2.  
  3. class Base {
  4.    protected:
  5.       virtual std::ostream & print(std::ostream& stream) const {
  6.          stream << "Base class output\n";
  7.          return stream;
  8.       }
  9.    public:
  10.  
  11.       // Define it only for the base class.
  12.       friend std::ostream & operator<<(std::ostream & stream, const Base & obj) {
  13.          return obj.print(stream);
  14.       }
  15.  
  16.       virtual ~Base() {}
  17. };
  18.  
  19. class A : public Base {
  20.  
  21.    std::ostream & print(std::ostream & stream) const {
  22.       this->Base::print(stream);
  23.       stream << "foo = " << foo << "\n";
  24.       return stream;
  25.    }
  26.  
  27.    int foo = 0;
  28.    public:
  29.    ~A() {}
  30. };
  31.  
  32. class B : public Base {
  33.  
  34.    std::ostream & print(std::ostream & stream) const {
  35.       this->Base::print(stream);
  36.       stream << "bar = " << bar << "\n";
  37.       return stream;
  38.    }
  39.  
  40.    int bar = 0;
  41.    public:
  42.    ~B() {}
  43. };
  44.  
  45.  
  46. int main(int argc, char * argv[]) {
  47.    Base * base = new Base();
  48.    A * a = new A();
  49.    B * b = new B();
  50.    Base * a_inside = dynamic_cast<Base *>(a);
  51.  
  52.    std::cout << *base << "\n";
  53.    std::cout << *a << "\n";
  54.    std::cout << *b << "\n";
  55.    std::cout << *a_inside << "\n";
  56.  
  57.    delete base;
  58.    delete a;
  59.    delete b;
  60.  
  61.    return 0;
  62. }
  63.  
Success #stdin #stdout 0s 4496KB
comments (?)
stdin
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Standard input is empty
stdout
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Base class output

Base class output
foo = 0

Base class output
bar = 0

Base class output
foo = 0
https://ideone.com/x6ti3W
language:
C++14 (gcc 8.3)
created:
7 years ago
visibility:
secret

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