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  1.     #include <iostream>
  2.     #include <functional>
  3.     #include <memory>
  4.     #include <map>
  5.     #include <unordered_map>
  6.     #include <vector>
  7.  
  8.     using namespace std;
  9.  
  10.     static constexpr long total_size = 1000000;
  11.  
  12.     template<typename T>
  13.     class CountingAllocator
  14.     {
  15.     public:
  16.         shared_ptr<size_t> d_max = make_shared<size_t>(0u);
  17.         using value_type = T;
  18.         using pointer = T*;
  19.  
  20.         CountingAllocator() = default;
  21.         template <typename S>
  22.         CountingAllocator(CountingAllocator<S> const& other): d_max(other.d_max) {}
  23.         size_t size() const { return *d_max; }
  24.         T* allocate(size_t size) {
  25.             size *= sizeof(T);
  26.             *d_max += size;
  27.             return reinterpret_cast<T*>(operator new(size));
  28.         }
  29.         void deallocate(void* ptr, size_t) {
  30.             operator delete(ptr);
  31.         }
  32.         friend bool operator== (CountingAllocator const& c0, CountingAllocator const& c1) {
  33.             return c0.d_max == c1.d_max;
  34.         } 
  35.  
  36.         friend bool operator!= (CountingAllocator const& c0, CountingAllocator const& c1) {
  37.             return !(c0 == c1);
  38.         }
  39.     };
  40.  
  41.     template <typename T>
  42.     void size(char const* name) {
  43.         CountingAllocator<typename T::value_type> allocator;
  44.         T m(allocator);
  45.         for (int i = 0; i != total_size; ++i) {
  46.             m[i] = i;
  47.         }
  48.         cout << name << "="  << allocator.size() << "\n";
  49.     }
  50.  
  51.     int main() {
  52.         size<map<long, long long, less<int>, CountingAllocator<pair<long const, long long>>>>("map");
  53.         size<unordered_map<long, long long, hash<long>, equal_to<long>, CountingAllocator<pair<long const, long long>>>>("unordered_map");
  54.         cout << "array=" << sizeof(long long[total_size]) << "\n";
  55. 	    return 0;
  56.     }
Success #stdin #stdout 0.5s 66028KB
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stdin
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Standard input is empty
stdout
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map=48000000
unordered_map=40654880
array=8000000
https://ideone.com/Ymb36c
language:
C++14 (clang 8.0)
created:
5 years ago
visibility:
public

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