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  1. #include <algorithm>
  2. #include <iomanip>
  3. #include <iostream>
  4. #include <map>
  5. #include <memory>
  6.  
  7.  
  8. class Base {
  9. public:
  10.     Base(int v) : id(v) {};
  11.     int id;  
  12. };
  13.  
  14. class Derived : public Base {
  15. public:
  16.     Derived(int v) : Base(v) {};
  17. };
  18.  
  19.  
  20. struct Less_id
  21. {
  22.   bool operator() (const std::shared_ptr<Derived> &lhs, const std::shared_ptr<Derived> &rhs) const
  23.   {
  24.     return lhs->id < rhs->id;
  25.   }
  26. };
  27.  
  28. typedef std::map<std::shared_ptr<Derived>, double, Less_id> Map;
  29.  
  30. Map::const_iterator find_base(const Map &map, const std::shared_ptr<Base> &base)
  31. {
  32.   auto it = std::lower_bound(
  33.     map.begin(), map.end(), base,
  34.     [](const Map::value_type &lhs, const std::shared_ptr<Base> &rhs)
  35.     { return lhs.first->id < rhs->id; }
  36.   );
  37.   if (it != map.end() && it->first->id == base->id)
  38.     return it;
  39.   else
  40.     return map.end();
  41. }
  42.  
  43.  
  44.  
  45.  
  46.  
  47. int main()
  48. {
  49.     Map m;
  50.     m.insert(std::make_pair(std::make_shared<Derived>(1), 10));
  51.     m.insert(std::make_pair(std::make_shared<Derived>(3), 30));
  52.     m.insert(std::make_pair(std::make_shared<Derived>(4), 40));
  53.     m.insert(std::make_pair(std::make_shared<Derived>(2), 20));
  54.  
  55.     auto b3 = std::make_shared<Base>(3);
  56.     auto it = find_base(m, b3);
  57.     std::cout << it->second << '\n';
  58.  
  59.     auto b5 = std::make_shared<Base>(5);
  60.     it = find_base(m, b5);
  61.     std::cout << std::boolalpha << (it == m.end()) << '\n';
  62.  
  63.     return 0;
  64. }
Success #stdin #stdout 0s 3432KB
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https://ideone.com/RWRtEq
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
public

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