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  1.     namespace ThirdPartyLib
  2.     {
  3.         template <typename T>
  4.         class SomeContainerFromAThirdPartyLib
  5.         {
  6.             public:
  7.                 typedef T ValueType;    //  not value_type! 
  8.                 //  no difference_type
  9.  
  10.                 class iterator
  11.                 {
  12.                     public:
  13.                         typedef T ValueType;    //  not value_type! 
  14.                         //  no difference_type
  15.  
  16.                         // obviously this is not how these would actually be implemented
  17.                         int operator != (const iterator& rhs) { return 0; }
  18.                         iterator& operator ++ () { return *this; }
  19.                         T operator * () { return T(); }
  20.                 };
  21.  
  22.                 // obviously this is not how these would actually be implemented      
  23.                 iterator begin() { return iterator(); }
  24.                 iterator end() { return iterator(); }
  25.         }; 
  26.     }
  27.  
  28.     #include <cstddef>
  29.     #include <iterator>
  30.  
  31.     namespace MyLib
  32.     {
  33.         template <typename T>
  34.         class iterator_adapter : public T
  35.         {
  36.             public:
  37.                 // replace the following with the appropriate types for the third party iterator
  38.                 typedef typename T::ValueType value_type;
  39.                 typedef std::ptrdiff_t difference_type;
  40.                 typedef typename T::ValueType* pointer;
  41.                 typedef typename T::ValueType& reference;
  42.                 typedef std::input_iterator_tag iterator_category;
  43.  
  44.                 explicit iterator_adapter(T t) : T(t) {}
  45.         };
  46.  
  47.         template <typename T>
  48.         class iterator_adapter<T*>
  49.         {
  50.         };
  51.     }
  52.  
  53.     #include <iostream>
  54.     #include <algorithm>
  55.  
  56.     using std::cout;
  57.     using std::endl;    
  58.  
  59.     template <typename iter>
  60.     typename MyLib::iterator_adapter<iter>::difference_type
  61.     count(iter begin, iter end, const typename iter::ValueType& val)
  62.     {
  63.         cout << "[in adapter version of count]";
  64.         return std::count(MyLib::iterator_adapter<iter>(begin), MyLib::iterator_adapter<iter>(end), val);
  65.     }
  66.  
  67.     using std::count;
  68.  
  69.     int main()
  70.     {
  71.         char a[] = "Hello, world";
  72.  
  73.         cout << "a=" << a << std::endl;
  74.         cout << "count(a, a + sizeof(a), 'l')=" << count(a, a + sizeof(a), 'l') << endl; 
  75.  
  76.         ThirdPartyLib::SomeContainerFromAThirdPartyLib<int> container;
  77.         cout << "count(container.begin(), container.end(), 0)=";
  78.         cout << count(container.begin(), container.end(), 0) << endl;
  79.  
  80.         return 0;
  81.     }
Success #stdin #stdout 0s 2896KB
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Standard input is empty
stdout
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a=Hello, world
count(a, a + sizeof(a), 'l')=3
count(container.begin(), container.end(), 0)=[in adapter version of count]0
https://ideone.com/gJyGxU
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
public

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