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  1. #include <iostream>
  2. #include <typeinfo>
  3.  
  4. struct Shape { virtual ~Shape() {}; };
  5. struct Circle : Shape {};
  6. struct Square : Shape {};
  7. struct 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.   std::cout << "Address of `s` = " << &s << std::endl;
  15.  
  16.   // (Since upcasting is such a safe and common
  17.   // operation, the cast becomes cluttering)
  18.  
  19.   // Static Navigation of class hierarchies
  20.   // requires extra type information:
  21.   // C++ RTTI
  22.   if (typeid(s) == typeid(Circle))
  23.   {
  24.     Circle & cp = static_cast<Circle&>(s);
  25.     std::cout << "It's a circle!" << std::endl;
  26.     std::cout << "Address = " << &cp << std::endl;
  27.   }
  28.   if (typeid(s) == typeid(Square))
  29.   {
  30.     Square & sp = static_cast<Square&>(s);
  31.     std::cout << "It's a square!" << std::endl;
  32.     std::cout << "Address = " << &sp << std::endl;
  33.   }
  34.   // Static navigation is ONLY an efficiency hack;
  35.   // dynamic_cast is always safer. However:
  36.   // Other & op = static_cast<Other&>(s);
  37.   // Conveniently gives an error message, while
  38.   // that would be undefined behavior (UB)!
  39.   // Other& op2 = (Other&)s;
  40.   // does not
  41.   // AND *nothing* is guaranteed if we uncomment the UB
  42.   // INCLUDING *anything* about the lines *before* the UB (yes, really!)
  43. }
Success #stdin #stdout 0s 2896KB
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Standard input is empty
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Address of `s` = 0xbfa675ec
It's a circle!
Address = 0xbfa675ec
https://ideone.com/sxNT7o
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
secret

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