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  1. #include <iostream>
  2. #include <typeinfo>
  3.  
  4. class Shape { public: virtual ~Shape() {}; };
  5. class Circle : public Shape {};
  6. class Square : public Shape {};
  7. class Other {};
  8.  
  9. int main() {
  10.   Circle c;
  11.   Shape* s = &c; // Upcast: normal and OK
  12.   // More explicit but unnecessary:
  13.   s = static_cast<Shape*>(&c);
  14.   // (Since upcasting is such a safe and common
  15.   // operation, the cast becomes cluttering)
  16.   Circle* cp = nullptr;
  17.   Square* sp = nullptr;
  18.   // Static Navigation of class hierarchies
  19.   // requires extra type information:
  20.   // C++ RTTI
  21.   if (typeid(*s) == typeid(Circle))
  22.     cp = static_cast<Circle*>(s);
  23.   if (typeid(*s) == typeid(Square))
  24.     sp = static_cast<Square*>(s);
  25.   std::cout << "cp = " << cp << std::endl;
  26.   std::cout << "sp = " << sp << std::endl;
  27.   if (cp) std::cout << "It's a circle!" << std::endl;
  28.   if (sp) std::cout << "It's a square!" << std::endl;
  29.   // Static navigation is ONLY an efficiency hack;
  30.   // dynamic_cast is always safer. However:
  31.   // Other* op = static_cast<Other*>(s);
  32.   // Conveniently gives an error message, while
  33.   // that would be undefined behavior (UB)!
  34.   // Other* op2 = (Other*)s;
  35.   // does not
  36.   // AND *nothing* is guaranteed if we uncomment the UB
  37.   // INCLUDING *anything* about the lines *before* the UB (yes, really!)
  38. }
Success #stdin #stdout 0s 2852KB
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Standard input is empty
stdout
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cp = 0xbff0ab6c
sp = 0
It's a circle!
https://ideone.com/dDRNFY
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
secret

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