Boost C++ Libraries

...one of the most highly regarded and expertly designed C++ library projects in the world. — Herb Sutter and Andrei Alexandrescu, C++ Coding Standards

This is the documentation for an old version of boost. Click here for the latest Boost documentation.

User Allocators

Introduction

Pool objects need to request memory blocks from the system, which the Pool then splits into chunks to allocate to the user. By specifying a UserAllocator template parameter to various Pool interfaces, users can control how those system memory blocks are allocated.

Semantics

*Symbol Table*
Symbol	Meaning
UserAllocator	A User Allocator type
block	value of type char *
n	value of type UserAllocator::size_type

*Typedefs*
Expression	Type
UserAllocator::size_type	An unsigned integral type that can represent the size of the largest object to be allocated
UserAllocator::difference_type	A signed integral type that can represent the difference of any two pointers

*Allocation and Deallocation*
Expression	Return Type	Pre-Condition/Notes
UserAllocator::malloc(n)	char *	Attempts to allocate n bytes from the system. Returns 0 if out-of-memory.
UserAllocator::free(block)	void	block must have been previously returned from a call to UserAllocator::malloc.

Provided Implementations

There are two UserAllocator classes provided. Both of them are in pool.hpp (see pool). The default value for the template parameter UserAllocator is always default_user_allocator_new_delete.

Synopsis

struct default_user_allocator_new_delete
{
  typedef std::size_t size_type;
  typedef std::ptrdiff_t difference_type;

  static char * malloc(const size_type bytes)
  { return new (std::nothrow) char[bytes]; }
  static void free(char * const block)
  { delete [] block; }
};

struct default_user_allocator_malloc_free
{
  typedef std::size_t size_type;
  typedef std::ptrdiff_t difference_type;

  static char * malloc(const size_type bytes)
  { return reinterpret_cast<char *>(std::malloc(bytes)); }
  static void free(char * const block)
  { std::free(block); }
};

This file can be redistributed and/or modified under the terms found in copyright.html

This software and its documentation is provided "as is" without express or implied warranty, and with no claim as to its suitability for any purpose.