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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd"><html><head><title>Memory Allocation Routines</title><style type="text/css">body { margin: auto; font-family: "Verdana" "sans-serif"; padding: 8px 1%;}a { color: #45735f }a:visited { color: #734559 }.logo { position:absolute; margin:3px; }.tagline { float:right; text-align:right; font-style:italic; width:240px; margin:12px; margin-top:58px;}.toolbar { font-variant: small-caps; text-align: center; line-height: 1.6em; margin: 0; padding:1px 8px;}.toolbar a { color: white; text-decoration: none; padding: 6px 12px; }.toolbar a:visited { color: white; }.toolbar a:hover { color: #80a796; background: white; }.content { margin: 5%; }.content dt { font-weight:bold; }.content dd { margin-bottom: 25px; margin-left:20%; }.content ul { padding:0px; padding-left: 15px; margin:0px; }/* rounded corners */.se { background: url(../images/se.png) 100% 100% no-repeat #80a796}.sw { background: url(../images/sw.png) 0% 100% no-repeat }.ne { background: url(../images/ne.png) 100% 0% no-repeat }.nw { background: url(../images/nw.png) 0% 0% no-repeat }</style><meta http-equiv="content-type" content="text/html; charset=UTF-8"> </head><body><div><!-- container div to satisfy validator --><a href="../index.html"><img class="logo" src="../images/SQLite.gif" alt="SQLite Logo" border="0"></a><div><!-- IE hack to prevent disappearing logo--></div><div class="tagline">Small. Fast. Reliable.<br>Choose any three.</div><table width=100% style="clear:both"><tr><td> <div class="se"><div class="sw"><div class="ne"><div class="nw"> <div class="toolbar"> <a href="../about.html">About</a> <a href="../sitemap.html">Sitemap</a> <a href="../docs.html">Documentation</a> <a href="../download.html">Download</a> <a href="../copyright.html">License</a> <a href="../news.html">News</a> <a href="http://www.sqlite.org/cvstrac/index">Developers</a> <a href="../support.html">Support</a> </div></div></div></div></div></td></tr></table> <a href="intro.html"><h2>SQLite C Interface</h2></a><h2>Memory Allocation Routines</h2><blockquote><pre>typedef struct sqlite3_mem_methods sqlite3_mem_methods;struct sqlite3_mem_methods { void *(*xMalloc)(int); /* Memory allocation function */ void (*xFree)(void*); /* Free a prior allocation */ void *(*xRealloc)(void*,int); /* Resize an allocation */ int (*xSize)(void*); /* Return the size of an allocation */ int (*xRoundup)(int); /* Round up request size to allocation size */ int (*xInit)(void*); /* Initialize the memory allocator */ void (*xShutdown)(void*); /* Deinitialize the memory allocator */ void *pAppData; /* Argument to xInit() and xShutdown() */};</pre></blockquote><p><b>Important:</b> This interface is <a href="../c3ref/experimental.html">experimental</a> and is subject to change without notice.</p><p>An instance of this object defines the interface between SQLiteand low-level memory allocation routines.</p><p>This object is used in only one place in the SQLite interface.A pointer to an instance of this object is the argument to<a href="../c3ref/config.html">sqlite3_config()</a> when the configuration option is<a href="../c3ref/c_config_getmalloc.html">SQLITE_CONFIG_MALLOC</a>. By creating an instance of this objectand passing it to <a href="../c3ref/config.html">sqlite3_config()</a> during configuration, anapplication can specify an alternative memory allocation subsystemfor SQLite to use for all of its dynamic memory needs.</p><p>Note that SQLite comes with a built-in memory allocator that isperfectly adequate for the overwhelming majority of applicationsand that this object is only useful to a tiny minority of applicationswith specialized memory allocation requirements. This object isalso used during testing of SQLite in order to specify an alternativememory allocator that simulates memory out-of-memory conditions inorder to verify that SQLite recovers gracefully from suchconditions.</p><p>The xMalloc, xFree, and xRealloc methods must work like themalloc(), free(), and realloc() functions from the standard library.</p><p>xSize should return the allocated size of a memory allocationpreviously obtained from xMalloc or xRealloc. The allocated sizeis always at least as big as the requested size but may be larger.</p><p>The xRoundup method returns what would be the allocated size ofa memory allocation given a particular requested size. Most memoryallocators round up memory allocations at least to the next multipleof 8. Some allocators round up to a larger multiple or to a power of 2.</p><p>The xInit method initializes the memory allocator. (For example,it might allocate any require mutexes or initialize internal datastructures. The xShutdown method is invoked (indirectly) by<a href="../c3ref/initialize.html">sqlite3_shutdown()</a> and should deallocate any resources acquiredby xInit. The pAppData pointer is used as the only parameter toxInit and xShutdown.</p><p>See also lists of <a href="objlist.html">Objects</a>, <a href="constlist.html">Constants</a>, and <a href="funclist.html">Functions</a>.</p><hr><small><i>This page last modified 2008/12/09 18:44:04 UTC</i></small></div></body></html>⌨️ 快捷键说明
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