| <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" |
| "http://www.w3.org/TR/html4/loose.dtd"> |
| |
| <html> |
| <head> |
| <meta http-equiv="Content-Language" content="en-us"> |
| <meta http-equiv="Content-Type" content="text/html; charset=us-ascii"> |
| <link href="../pool.css" rel="stylesheet" type="text/css"> |
| |
| <title>Pool</title> |
| </head> |
| |
| <body> |
| <img src="../../../../boost.png" width="276" height="86" alt="C++ Boost"> |
| |
| <h1 align="center">User Allocators</h1> |
| |
| <h2>Introduction</h2> |
| |
| <p>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 |
| <span class="code">UserAllocator</span> template parameter to various Pool |
| interfaces, users can control how those system memory blocks are |
| allocated.</p> |
| |
| <h2>Semantics</h2> |
| |
| <table border align="center" summary=""> |
| <caption> |
| <em>Symbol Table</em> |
| </caption> |
| |
| <tr> |
| <th>Symbol</th> |
| |
| <th>Meaning</th> |
| </tr> |
| |
| <tr> |
| <td class="code">UserAllocator</td> |
| |
| <td>A User Allocator type</td> |
| </tr> |
| |
| <tr> |
| <td class="code">block</td> |
| |
| <td>value of type <span class="code">char *</span></td> |
| </tr> |
| |
| <tr> |
| <td class="code">n</td> |
| |
| <td>value of type <span class= |
| "code">UserAllocator::size_type</span></td> |
| </tr> |
| </table><br> |
| |
| <table border align="center" summary=""> |
| <caption> |
| <em>Typedefs</em> |
| </caption> |
| |
| <tr> |
| <th>Expression</th> |
| |
| <th>Type</th> |
| </tr> |
| |
| <tr> |
| <td class="code">UserAllocator::size_type</td> |
| |
| <td>An unsigned integral type that can represent the size of the |
| largest object to be allocated</td> |
| </tr> |
| |
| <tr> |
| <td class="code">UserAllocator::difference_type</td> |
| |
| <td>A signed integral type that can represent the difference of any two |
| pointers</td> |
| </tr> |
| </table><br> |
| |
| <table border align="center" summary=""> |
| <caption> |
| <em>Allocation and Deallocation</em> |
| </caption> |
| |
| <tr> |
| <th>Expression</th> |
| |
| <th>Return Type</th> |
| |
| <th>Pre-Condition/Notes</th> |
| </tr> |
| |
| <tr> |
| <td class="code">UserAllocator::malloc(n)</td> |
| |
| <td class="code">char *</td> |
| |
| <td>Attempts to allocate <span class="code">n</span> bytes from the |
| system. Returns 0 if out-of-memory.</td> |
| </tr> |
| |
| <tr> |
| <td class="code">UserAllocator::free(block)</td> |
| |
| <td class="code">void</td> |
| |
| <td><span class="code">block</span> must have been previously returned |
| from a call to <span class="code">UserAllocator::malloc</span>.</td> |
| </tr> |
| </table> |
| |
| <h2>Provided Implementations</h2> |
| |
| <p>There are two <span class="code">UserAllocator</span> classes provided. |
| Both of them are in pool.hpp (see <a href="pool.html">pool</a>). The |
| default value for the template parameter <span class= |
| "code">UserAllocator</span> is always <span class= |
| "code">default_user_allocator_new_delete</span>.</p> |
| |
| <h3>Synopsis</h3> |
| <pre class="code"> |
| 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); } |
| }; |
| </pre> |
| <hr> |
| |
| <p><a href="http://validator.w3.org/check?uri=referer"><img border="0" src= |
| "../../../../doc/images/valid-html401.png" alt="Valid HTML 4.01 Transitional" |
| height="31" width="88"></a></p> |
| |
| <p>Revised |
| <!--webbot bot="Timestamp" s-type="EDITED" s-format="%d %B, %Y" startspan -->05 |
| December, 2006<!--webbot bot="Timestamp" endspan i-checksum="38516" --></p> |
| |
| <p><i>Copyright © 2000, 2001 Stephen Cleary (scleary AT jerviswebb DOT |
| com)</i></p> |
| |
| <p><i>Distributed under the Boost Software License, Version 1.0. (See |
| accompanying file <a href="../../../../LICENSE_1_0.txt">LICENSE_1_0.txt</a> |
| or copy at <a href= |
| "http://www.boost.org/LICENSE_1_0.txt">http://www.boost.org/LICENSE_1_0.txt</a>)</i></p> |
| </body> |
| </html> |
