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  1. // Demonstrating STL vector constructors with a user-defined
  2. // type and showing copying explicitly
  3. #include <iostream>
  4. #include <cassert>
  5. #include <vector>
  6. using namespace std;
  7.  
  8. class U { 
  9. public: 
  10.   unsigned long id;
  11.   unsigned long generation;
  12.   static unsigned long total_copies;
  13.   U() : id(0), generation(0) { }
  14.   U(unsigned long n) : id(n), generation(0) { }
  15.   U(const U& z) : id(z.id), generation(z.generation + 1) { 
  16.     ++total_copies;
  17.   } 
  18. };
  19.  
  20. bool operator==(const U& x, const U& y) 
  21. { 
  22.   return x.id == y.id; 
  23. }
  24.  
  25. bool operator!=(const U& x, const U& y) 
  26. { 
  27.   return x.id != y.id; 
  28. }
  29.  
  30. unsigned long U::total_copies = 0;
  31.  
  32. int main() 
  33. {
  34.   cout << "Demonstrating STL vector constructors with a \n"
  35.        << "user-defined type and showing copying explicitly \n" << endl;
  36.   vector<U> vector1, vector2(3);
  37.  
  38.   assert (vector1.size() == 0);
  39.   assert (vector2.size() == 3);
  40.  
  41.   assert (vector2[0] == U() && vector2[1] == U() &&
  42.           vector2[2] == U());
  43.  
  44.   for (int i = 0; i != 3; ++i)
  45.     cout << "vector2[" << i << "].generation: " 
  46.          << vector2[i].generation << endl;
  47.  
  48.   cout << "Total copies: " << U::total_copies << endl;
  49.  
  50.   cin.get();
  51.   return 0;
  52. }
  53.  
Success #stdin #stdout 0s 3464KB
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Demonstrating STL vector constructors with a 
user-defined type and showing copying explicitly 

vector2[0].generation: 1
vector2[1].generation: 1
vector2[2].generation: 1
Total copies: 3
https://ideone.com/Tem3Bm
language:
C++14 (clang 8.0)
created:
8 years ago
visibility:
public

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