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Class template allocator

boost::container::allocator

Synopsis

// In header: <boost/container/allocator.hpp>

template<typename T> 
class allocator {
public:
  // types
  typedef T              value_type;     
  typedef T *            pointer;        
  typedef const T *      const_pointer;  
  typedef T &            reference;      
  typedef const T &      const_reference;
  typedef std::size_t    size_type;      
  typedef std::ptrdiff_t difference_type;
  typedef unspecified    version;        

  // member classes/structs/unions
  template<typename T2> 
  struct rebind {
    // types
    typedef allocator< T2, Version, AllocationDisableMask > other;
  };

  // construct/copy/destruct
  allocator() noexcept;
  allocator(const allocator &) noexcept;
  template<typename T2> allocator(const allocator< T2 > &) noexcept;

  // public member functions
  pointer allocate(size_type, const void * = 0);
  void deallocate(pointer, size_type) noexcept;
  size_type max_size() const noexcept;
  std::pair< pointer, bool > 
  allocation_command(allocation_type, size_type, size_type, size_type &, 
                     pointer = pointer());
  size_type size(pointer) const noexcept;
  pointer allocate_one();
  void allocate_individual(std::size_t, multiallocation_chain &);
  void deallocate_one(pointer) noexcept;
  void deallocate_individual(multiallocation_chain &) noexcept;
  void allocate_many(size_type, std::size_t, multiallocation_chain &);
  void allocate_many(const size_type *, size_type, multiallocation_chain &);
  void deallocate_many(multiallocation_chain &) noexcept;

  // friend functions
  friend void swap(self_t &, self_t &) noexcept;
  friend bool operator==(const allocator &, const allocator &) noexcept;
  friend bool operator!=(const allocator &, const allocator &) noexcept;

  // private member functions
  std::pair< pointer, bool > 
  priv_allocation_command(allocation_type, std::size_t, std::size_t, 
                          std::size_t &, void *);
};

Description

allocator public construct/copy/destruct

  1. allocator() noexcept;

    Default constructor Never throws

  2. allocator(const allocator &) noexcept;

    Constructor from other allocator. Never throws

  3. template<typename T2> allocator(const allocator< T2 > &) noexcept;

    Constructor from related allocator. Never throws

allocator public member functions

  1. pointer allocate(size_type count, const void * hint = 0);

    Allocates memory for an array of count elements. Throws std::bad_alloc if there is no enough memory If Version is 2, this allocated memory can only be deallocated with deallocate() or (for Version == 2) deallocate_many()

  2. void deallocate(pointer ptr, size_type) noexcept;

    Deallocates previously allocated memory. Never throws

  3. size_type max_size() const noexcept;

    Returns the maximum number of elements that could be allocated. Never throws

  4. std::pair< pointer, bool > 
    allocation_command(allocation_type command, size_type limit_size, 
                       size_type preferred_size, size_type & received_size, 
                       pointer reuse = pointer());

    An advanced function that offers in-place expansion shrink to fit and new allocation capabilities. Memory allocated with this function can only be deallocated with deallocate() or deallocate_many(). This function is available only with Version == 2

  5. size_type size(pointer p) const noexcept;

    Returns maximum the number of objects the previously allocated memory pointed by p can hold. Memory must not have been allocated with allocate_one or allocate_individual. This function is available only with Version == 2

  6. pointer allocate_one();

    Allocates just one object. Memory allocated with this function must be deallocated only with deallocate_one(). Throws bad_alloc if there is no enough memory This function is available only with Version == 2

  7. void allocate_individual(std::size_t num_elements, 
                             multiallocation_chain & chain);

    Allocates many elements of size == 1. Elements must be individually deallocated with deallocate_one() This function is available only with Version == 2

  8. void deallocate_one(pointer p) noexcept;

    Deallocates memory previously allocated with allocate_one(). You should never use deallocate_one to deallocate memory allocated with other functions different from allocate_one() or allocate_individual.

  9. void deallocate_individual(multiallocation_chain & chain) noexcept;

    Deallocates memory allocated with allocate_one() or allocate_individual(). This function is available only with Version == 2

  10. void allocate_many(size_type elem_size, std::size_t n_elements, 
                       multiallocation_chain & chain);

    Allocates many elements of size elem_size. Elements must be individually deallocated with deallocate() This function is available only with Version == 2

  11. void allocate_many(const size_type * elem_sizes, size_type n_elements, 
                       multiallocation_chain & chain);

    Allocates n_elements elements, each one of size elem_sizes[i] Elements must be individually deallocated with deallocate() This function is available only with Version == 2

  12. void deallocate_many(multiallocation_chain & chain) noexcept;

    Deallocates several elements allocated by allocate_many(), allocate(), or allocation_command(). This function is available only with Version == 2

allocator friend functions

  1. friend void swap(self_t &, self_t &) noexcept;

    Swaps two allocators, does nothing because this allocator is stateless

  2. friend bool operator==(const allocator &, const allocator &) noexcept;

    An allocator always compares to true, as memory allocated with one instance can be deallocated by another instance

  3. friend bool operator!=(const allocator &, const allocator &) noexcept;

    An allocator always compares to false, as memory allocated with one instance can be deallocated by another instance

allocator private member functions

  1. std::pair< pointer, bool > 
    priv_allocation_command(allocation_type command, std::size_t limit_size, 
                            std::size_t preferred_size, 
                            std::size_t & received_size, void * reuse_ptr);

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