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  1. #include <iostream>
  2. #include <vector>
  3. #include <string>
  4.  
  5. template<typename T>
  6. class CAllocator
  7. {
  8.     private:
  9.         std::size_t size;
  10.         T* data = nullptr;
  11.  
  12.     public:
  13.         typedef T* pointer;
  14.         typedef const T* const_pointer;
  15.  
  16.         typedef T& reference;
  17.         typedef const T& const_reference;
  18.  
  19.         typedef std::size_t size_type;
  20.         typedef std::ptrdiff_t difference_type;
  21.  
  22.         typedef T value_type;
  23.  
  24.  
  25.         CAllocator() {}
  26.         CAllocator(pointer data_ptr, size_type max_size) noexcept : size(max_size), data(data_ptr) {};
  27.  
  28.         template<typename U>
  29.         CAllocator(const CAllocator<U>& other) noexcept {};
  30.  
  31.         CAllocator(const CAllocator &other) : size(other.size), data(other.data) {}
  32.  
  33.         template<typename U>
  34.         struct rebind {typedef CAllocator<U> other;};
  35.  
  36.         pointer allocate(size_type n, const void* hint = 0) {return &data[0];}
  37.         void deallocate(void* ptr, size_type n) {}
  38.         size_type max_size() const {return size;}
  39. };
  40.  
  41. template <typename T, typename U>
  42. inline bool operator == (const CAllocator<T>&, const CAllocator<U>&) {return true;}
  43.  
  44. template <typename T, typename U>
  45. inline bool operator != (const CAllocator<T>& a, const CAllocator<U>& b) {return !(a == b);}
  46.  
  47. struct RepBase
  48. {
  49.     std::size_t		length;
  50.     std::size_t		capacity;
  51.     std::int16_t  	refcount;
  52. };
  53.  
  54. int main()
  55. {
  56. 	typedef std::basic_string<char, std::char_traits<char>, CAllocator<char>> CAString;
  57.  
  58.     const int size = 1024;
  59. 	char ptr[size] = {0};
  60.  
  61. 	CAString str(CAllocator<char>(&ptr[0], size));
  62. 	str.append("hello");
  63.  
  64.     std::cout<<&ptr[sizeof(RepBase)];
  65. }
  66.  
Success #stdin #stdout 0s 3340KB
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Standard input is empty
stdout
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hello
https://ideone.com/QWtxWg
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
secret

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