internals2.structure.basics.html
来自「php的帮助文档,涉及到PHP的案例和基本语法,以及实际应用内容」· HTML 代码 · 共 148 行
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"><html> <head> <title>Basic constructs</title> <meta http-equiv="content-type" content="text/html; charset=UTF-8"> </head> <body><div style="text-align: center;"> <div class="prev" style="text-align: left; float: left;"><a href="internals2.structure.html">Extension structure</a></div> <div class="next" style="text-align: right; float: right;"><a href="internals2.structure.modstruct.html">The zend_module structure</a></div> <div class="up"><a href="internals2.structure.html">Extension structure</a></div> <div class="home"><a href="index.html">PHP Manual</a></div></div><hr /><div id="internals2.structure.basics" class="sect1"> <h2 class="title">Basic constructs</h2> <p class="simpara"> C is a very low-level language by modern definitions. This means that it has no built-in support for many features that PHP takes for granted, such as reflection, dynamic module loading, bounds checking, threadsafe data management and various useful data structures including linked lists and hash tables. At the same time, C is a common denominator of language support and functionality. Given enough work, none of these concepts are impossible; the Zend Engine uses them all. </p> <p class="simpara"> A lot of effort has gone into making the Zend API both extensible and understandable, but C forces certain necessary declarations upon any extension that to an inexperienced eye seem redundant or plain unnecessary. All of those constructs, detailed in this section, are "write once and forget" in Zend Engine 2 and 3. Here are some excerpts from the pregenerated <var class="filename">php_counter.h</var> and <var class="filename">counter.c</var> files created by PHP 5.3's <strong class="command">ext_skel</strong>, showing the pregenerated declarations: </p> <blockquote><p><b class="note">Note</b>: <span class="simpara"> The astute reader will notice that there are several delcarations in the real files that aren't shown here. Those declaractions are specific to various Zend subsystems and are discussed elsewhere as appropriate. </span> </p></blockquote> <div class="example-contents"><pre><div class="cdata"><pre>extern zend_module_entry counter_module_entry;#define phpext_counter_ptr &counter_module_entry#ifdef PHP_WIN32# define PHP_COUNTER_API __declspec(dllexport)#elif defined(__GNUC__) && __GNUC__ >= 4# define PHP_COUNTER_API __attribute__ ((visibility("default")))#else# define PHP_COUNTER_API#endif#ifdef ZTS#include "TSRM.h"#endif</pre></div></pre></div> <div class="example-contents"><pre><div class="cdata"><pre>#ifdef HAVE_CONFIG_H#include "config.h"#endif#include "php.h"#include "php_ini.h"#include "ext/standard/info.h"#include "php_counter.h"/* ... */#ifdef COMPILE_DL_COUNTERZEND_GET_MODULE(counter)#endif</pre></div></pre></div> <ul class="itemizedlist"> <li class="listitem"> <span class="simpara"> The lines concerning <i>counter_module_entry</i> declare a global variable, and a macroed pointer to it, which contains the <i>zend_module_entry</i> for the extension. Despite the later discussion regarding the drawbacks of "true" globals, this usage is intentional; Zend takes precautions to avoid misusing this variable. </span> </li> <li class="listitem"> <span class="simpara"> <b><tt>PHP_COUNTER_API</tt></b> is declared for use by non-PHP functions the module intends to export for the use of other modules. The counter extension doesn't declare any of these, and in the final version of the header file, this macro has been removed. The <b><tt>PHPAPI</tt></b> macro is declared identically elsewhere and is used by the standard extension to make the <a href="function.phpinfo.html" class="function">phpinfo()</a> utility functions available to other extensions. </span> </li> <li class="listitem"> <span class="simpara"> The include of <var class="filename">TSRM.h</var> is skipped if PHP, or the extension, isn't being compiled with thread-safety, since in that case TSRM isn't used. </span> </li> <li class="listitem"> <span class="simpara"> A standard list of includes, especially the extension's own <var class="filename">php_counter.h</var>, is given. <var class="filename">config.h</var> gives the extension access to determinations made by <strong class="command">configure</strong>. <var class="filename">php.h</var> is the gateway to the entire PHP and Zend APIs. <var class="filename">php_ini.h</var> adds the APIs for runtime configuration (INI) entries. Not all extensions will use this. Finally, <var class="filename">ext/standard/info.h</var> imports the aforementioned <a href="function.phpinfo.html" class="function">phpinfo()</a> utility API. </span> </li> <li class="listitem"> <span class="simpara"> <b><tt>COMPILE_DL_COUNTER</tt></b> will only be defined by <strong class="command">configure</strong> if the counter extension is both enabled and wants to be built as a dynamically loadable module instead of being statically linked into PHP. <b><tt>ZEND_GET_MODULE</tt></b> defines a tiny function which Zend can use to get the extension's <i>zend_module_entry</i> at runtime. </span> <blockquote><p><b class="note">Note</b>: <span class="simpara"> The astute reader who has peeked into <var class="filename">main/php_config.h</var> after trying to build with the counter module enabled statically may have noticed that there is also a <b><tt>HAVE_COUNTER</tt></b> constant defined that the source code doesn't check for. There's a simple reason this check isn't done: It's unnecessary. If the extension isn't enabled, the source file will never be compiled. </span> </p></blockquote> </li> </ul> </div><hr /><div style="text-align: center;"> <div class="prev" style="text-align: left; float: left;"><a href="internals2.structure.html">Extension structure</a></div> <div class="next" style="text-align: right; float: right;"><a href="internals2.structure.modstruct.html">The zend_module structure</a></div> <div class="up"><a href="internals2.structure.html">Extension structure</a></div> <div class="home"><a href="index.html">PHP Manual</a></div></div></body></html>⌨️ 快捷键说明
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