📄 control-structures.declare.html
字号:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"><html> <head> <title>declare</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="control-structures.switch.html">switch</a></div> <div class="next" style="text-align: right; float: right;"><a href="function.return.html">return</a></div> <div class="up"><a href="language.control-structures.html">Control Structures</a></div> <div class="home"><a href="index.html">PHP Manual</a></div></div><hr /><div id="control-structures.declare" class="sect1"> <h2 class="title"><i>declare</i></h2> <p class="para"> The <i>declare</i> construct is used to set execution directives for a block of code. The syntax of <i>declare</i> is similar to the syntax of other flow control constructs: <div class="informalexample"> <div class="example-contents"><div class="cdata"><pre>declare (directive) statement</pre></div> </div> </div> </p> <p class="para"> The <i>directive</i> section allows the behavior of the <i>declare</i> block to be set. Currently only one directive is recognized: the <i>ticks</i> directive. (See below for more information on the <a href="control-structures.declare.html#control-structures.declare.ticks" class="link">ticks</a> directive) </p> <p class="para"> The <i>statement</i> part of the <i>declare</i> block will be executed -- how it is executed and what side effects occur during execution may depend on the directive set in the <i>directive</i> block. </p> <p class="para"> The <i>declare</i> construct can also be used in the global scope, affecting all code following it. <div class="informalexample"> <div class="example-contents"><div class="phpcode"><code><span style="color: #000000"><span style="color: #0000BB"><?php<br /></span><span style="color: #FF8000">// these are the same:<br /><br />// you can use this:<br /></span><span style="color: #007700">declare(</span><span style="color: #0000BB">ticks</span><span style="color: #007700">=</span><span style="color: #0000BB">1</span><span style="color: #007700">) {<br /> </span><span style="color: #FF8000">// entire script here<br /></span><span style="color: #007700">}<br /><br /></span><span style="color: #FF8000">// or you can use this:<br /></span><span style="color: #007700">declare(</span><span style="color: #0000BB">ticks</span><span style="color: #007700">=</span><span style="color: #0000BB">1</span><span style="color: #007700">);<br /></span><span style="color: #FF8000">// entire script here<br /></span><span style="color: #0000BB">?></span></span></code></div> </div> </div> </p> <div id="control-structures.declare.ticks" class="sect2"> <h3 class="title">Ticks</h3> <div class="caution"><b class="caution">Caution</b> <p class="simpara"> As of PHP 5.3.0 ticks are deprecated and will be removed in PHP 6.0.0. </p> </div> <p class="para">A tick is an event that occurs for every <var class="varname">N</var> low-level statements executed by the parser within the <i>declare</i> block. The value for <var class="varname">N</var> is specified using <code class="code">ticks=<var class="varname">N</var></code> within the <i>declare</i> blocks's <i>directive</i> section. </p> <p class="para"> The event(s) that occur on each tick are specified using the <a href="function.register-tick-function.html" class="function">register_tick_function()</a>. See the example below for more details. Note that more than one event can occur for each tick. </p> <p class="para"> <div class="example"> <p><b>Example #1 Profile a section of PHP code</b></p> <div class="example-contents"><div class="phpcode"><code><span style="color: #000000"><span style="color: #0000BB"><?php<br /></span><span style="color: #FF8000">// A function that records the time when it is called<br /></span><span style="color: #007700">function </span><span style="color: #0000BB">profile</span><span style="color: #007700">(</span><span style="color: #0000BB">$dump </span><span style="color: #007700">= </span><span style="color: #0000BB">FALSE</span><span style="color: #007700">)<br />{<br /> static </span><span style="color: #0000BB">$profile</span><span style="color: #007700">;<br /><br /> </span><span style="color: #FF8000">// Return the times stored in profile, then erase it<br /> </span><span style="color: #007700">if (</span><span style="color: #0000BB">$dump</span><span style="color: #007700">) {<br /> </span><span style="color: #0000BB">$temp </span><span style="color: #007700">= </span><span style="color: #0000BB">$profile</span><span style="color: #007700">;<br /> unset(</span><span style="color: #0000BB">$profile</span><span style="color: #007700">);<br /> return </span><span style="color: #0000BB">$temp</span><span style="color: #007700">;<br /> }<br /><br /> </span><span style="color: #0000BB">$profile</span><span style="color: #007700">[] = </span><span style="color: #0000BB">microtime</span><span style="color: #007700">();<br />}<br /><br /></span><span style="color: #FF8000">// Set up a tick handler<br /></span><span style="color: #0000BB">register_tick_function</span><span style="color: #007700">(</span><span style="color: #DD0000">"profile"</span><span style="color: #007700">);<br /><br /></span><span style="color: #FF8000">// Initialize the function before the declare block<br /></span><span style="color: #0000BB">profile</span><span style="color: #007700">();<br /><br /></span><span style="color: #FF8000">// Run a block of code, throw a tick every 2nd statement<br /></span><span style="color: #007700">declare(</span><span style="color: #0000BB">ticks</span><span style="color: #007700">=</span><span style="color: #0000BB">2</span><span style="color: #007700">) {<br /> for (</span><span style="color: #0000BB">$x </span><span style="color: #007700">= </span><span style="color: #0000BB">1</span><span style="color: #007700">; </span><span style="color: #0000BB">$x </span><span style="color: #007700">< </span><span style="color: #0000BB">50</span><span style="color: #007700">; ++</span><span style="color: #0000BB">$x</span><span style="color: #007700">) {<br /> echo </span><span style="color: #0000BB">similar_text</span><span style="color: #007700">(</span><span style="color: #0000BB">md5</span><span style="color: #007700">(</span><span style="color: #0000BB">$x</span><span style="color: #007700">), </span><span style="color: #0000BB">md5</span><span style="color: #007700">(</span><span style="color: #0000BB">$x</span><span style="color: #007700">*</span><span style="color: #0000BB">$x</span><span style="color: #007700">)), </span><span style="color: #DD0000">"<br />;"</span><span style="color: #007700">;<br /> }<br />}<br /><br /></span><span style="color: #FF8000">// Display the data stored in the profiler<br /></span><span style="color: #0000BB">print_r</span><span style="color: #007700">(</span><span style="color: #0000BB">profile</span><span style="color: #007700">(</span><span style="color: #0000BB">TRUE</span><span style="color: #007700">));<br /></span><span style="color: #0000BB">?></span></span></code></div> </div> </div> The example profiles the PHP code within the 'declare' block, recording the time at which every second low-level statement in the block was executed. This information can then be used to find the slow areas within particular segments of code. This process can be performed using other methods: using ticks is more convenient and easier to implement. </p> <p class="simpara"> Ticks are well suited for debugging, implementing simple multitasking, background I/O and many other tasks. </p> <p class="simpara"> See also <a href="function.register-tick-function.html" class="function">register_tick_function()</a> and <a href="function.unregister-tick-function.html" class="function">unregister_tick_function()</a>. </p> </div> </div><hr /><div style="text-align: center;"> <div class="prev" style="text-align: left; float: left;"><a href="control-structures.switch.html">switch</a></div> <div class="next" style="text-align: right; float: right;"><a href="function.return.html">return</a></div> <div class="up"><a href="language.control-structures.html">Control Structures</a></div> <div class="home"><a href="index.html">PHP Manual</a></div></div></body></html>⌨️ 快捷键说明
复制代码
Ctrl + C
搜索代码
Ctrl + F
全屏模式
F11
切换主题
Ctrl + Shift + D
显示快捷键
?
增大字号
Ctrl + =
减小字号
Ctrl + -