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  1. #include <iostream>
  2. #include <memory>
  3. #include <vector>
  4.  
  5. typedef std::vector<class A*> AVector;
  6.  
  7. class A
  8. {
  9. protected: // so B can access it.
  10.     int m_i;
  11. public:
  12.     A(int i_) : m_i(i_)
  13.     {
  14.         std::cout << "CTor'd A(i) " << (void*)this
  15.                   << " with " << m_i << std::endl;
  16.     }
  17.     A(int i_, bool) : m_i(i_)
  18.     {
  19.         std::cout << "CTor'd A(i, b) " << (void*)this
  20.                   << " with " << m_i << std::endl;
  21.  
  22.     }
  23.  
  24.     virtual ~A()
  25.     {
  26.         std::cout << "DTor'd A " << (void*)this << " with " << m_i << std::endl;
  27.     }
  28. };
  29.  
  30. class B : public A
  31. {
  32.     int m_j;
  33. public:
  34.     B(int i_, int j_) : A(i_, true), m_j(j_)
  35.     {
  36.         std::cout << "CTor'd B(i, j) " << (void*)this
  37.                   << " with " << m_i << ", " << m_j << std::endl;
  38.     }
  39.  
  40.     virtual ~B()
  41.     {
  42.         std::cout << "DTor'd B " << (void*)this
  43.                   << " with " << m_i << ", " << m_j << std::endl;
  44.     }
  45. };
  46.  
  47. int main()
  48. {
  49.     AVector avec;
  50.  
  51.     std::cout << "create A(1)" << std::endl;
  52.     avec.push_back(new A(1)); // allocated an "A" on the heap.
  53.     std::cout << "create B(2, 1)" << std::endl;
  54.     avec.push_back(new B(2, 1)); // allocated a "B" on the heap.
  55.     std::cout << "create B(2, 2)" << std::endl;
  56.     avec.push_back(new B(2, 2));
  57.     std::cout << "create A(3) " << std::endl;
  58.     avec.push_back(new A(3));
  59.     std::cout << "populated avec" << std::endl;
  60.  
  61.     A* ptr = avec[2]; // take the pointer of what is actually a B
  62.     avec.erase(avec.begin() + 2); // remove it from the vector.
  63.     std::cout << "removed entry 2 from the vector" << std::endl;
  64.     // 'ptr' is still valid because it's an allocation, and C++ doesn't
  65.     // garbage collect heap allocations. We have to 'delete' it ourselves.
  66.     // Also note that because A and B have virtual destructors,
  67.     // you will see both of them called.
  68.     delete ptr;
  69.  
  70.     // Now watch what DOESN'T happen as we exit.
  71.     // everything we CTOR'd that doesn't get DTORd is a leak.
  72.     return 0;
  73. }
  74.  
Success #stdin #stdout 0s 3476KB
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stdin
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Standard input is empty
stdout
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create A(1)
CTor'd A(i) 0x9d94008 with 1
create B(2, 1)
CTor'd A(i, b) 0x9d94028 with 2
CTor'd B(i, j) 0x9d94028 with 2, 1
create B(2, 2)
CTor'd A(i, b) 0x9d94018 with 2
CTor'd B(i, j) 0x9d94018 with 2, 2
create A(3) 
CTor'd A(i) 0x9d94038 with 3
populated avec
removed entry 2 from the vector
DTor'd B 0x9d94018 with 2, 2
DTor'd A 0x9d94018 with 2
https://ideone.com/lo1G7I
language:
C++ (gcc 8.3)
created:
10 years ago
visibility:
public

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