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  1. #include <iostream>
  2. using namespace std;
  3.  
  4. template <typename T, typename U>
  5. T&& Forward(U&& arg) {
  6.   return static_cast<T&&>(arg);
  7. }
  8.  
  9. class Container
  10. {
  11.     int data_;
  12. public:
  13.     explicit Container(int data = 1) // Set the data variable
  14.         : data_(data) {}
  15.     ~Container() {data_ = -1;} // When destructed, first set the data to -1
  16.  
  17.     void test()
  18.     {
  19.         if (data_ <= 0)
  20.             std::cout << "OPS! A is destructed!\n";
  21.         else
  22.             std::cout << "A = " << data_ << '\n';
  23.     }
  24. };
  25.  
  26. // This class has a reference to the data object
  27. class Reference_To_Container_Wrapper
  28. {
  29.     const Container& a_;
  30. public:
  31.     explicit Reference_To_Container_Wrapper(const Container& a) : a_(a) {}
  32.  
  33. 	// (I) This line causes problems! This "Container" returned will be destroyed and cause troubles!
  34.     const Container get() const {return a_;} // Build a new Container out of the reference and return it
  35. };
  36.  
  37. template <class T>
  38. struct ReferenceContainer
  39. {
  40.     T should_be_valid_lvalue_ref; 
  41.  
  42.     template <class U> // U = Reference_To_Container_Wrapper
  43.         ReferenceContainer(U&& u) : 
  44.          // We store a l-value reference to a container, but the container is from line (I)
  45.          // and thus will soon get destroyed and we'll have a dangling reference
  46.          should_be_valid_lvalue_ref(Forward<T>(std::move(u).get())) {}
  47. };
  48.  
  49. int main() {
  50.  
  51. 	Container a(42); // This lives happily with perfect valid data
  52. 	ReferenceContainer<const Container&> rc( (Reference_To_Container_Wrapper(a)) ); // Parenthesis necessary otherwise most vexing parse will think this is a function pointer..
  53. 	// rc now has a dangling reference
  54. 	Container newContainer = rc.should_be_valid_lvalue_ref; // From reference to Container
  55. 	newContainer.test();
  56.  
  57. 	return 0;
  58. }
Success #stdin #stdout 0s 3296KB
comments (?)
stdin 
Standard input is empty
stdout 
OPS! A is destructed!
https://ideone.com/SyUXss
language:
C++14 (gcc 8.3)
created:
11 years ago
visibility:
public

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