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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

</code></div>
    </div>

   </div>
  </div>

  <div id="language.oop5.magic.tostring" class="sect2">
   <h3 class="title"><i>__toString</i></h3>
   <p class="para">
    The <i>__toString</i> method allows a class to decide
    how it will react when it is converted to a string.
   </p>
   <div class="example">
    <p><b>Example #2 Simple example</b></p>
    <div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB">&lt;?php<br /></span><span style="color: #FF8000">//&nbsp;Declare&nbsp;a&nbsp;simple&nbsp;class<br /></span><span style="color: #007700">class&nbsp;</span><span style="color: #0000BB">TestClass<br /></span><span style="color: #007700">{<br />&nbsp;&nbsp;&nbsp;&nbsp;public&nbsp;</span><span style="color: #0000BB">$foo</span><span style="color: #007700">;<br /><br />&nbsp;&nbsp;&nbsp;&nbsp;public&nbsp;function&nbsp;</span><span style="color: #0000BB">__construct</span><span style="color: #007700">(</span><span style="color: #0000BB">$foo</span><span style="color: #007700">)&nbsp;{<br />&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span style="color: #0000BB">$this</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">foo&nbsp;</span><span style="color: #007700">=&nbsp;</span><span style="color: #0000BB">$foo</span><span style="color: #007700">;<br />&nbsp;&nbsp;&nbsp;&nbsp;}<br /><br />&nbsp;&nbsp;&nbsp;&nbsp;public&nbsp;function&nbsp;</span><span style="color: #0000BB">__toString</span><span style="color: #007700">()&nbsp;{<br />&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;return&nbsp;</span><span style="color: #0000BB">$this</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">foo</span><span style="color: #007700">;<br />&nbsp;&nbsp;&nbsp;&nbsp;}<br />}<br /><br /></span><span style="color: #0000BB">$class&nbsp;</span><span style="color: #007700">=&nbsp;new&nbsp;</span><span style="color: #0000BB">TestClass</span><span style="color: #007700">(</span><span style="color: #DD0000">'Hello'</span><span style="color: #007700">);<br />echo&nbsp;</span><span style="color: #0000BB">$class</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">?&gt;</span>
</span>
</code></div>
    </div>

    <div class="example-contents"><p>The above example will output:</p></div>
    <div class="example-contents"><pre>
<div class="cdata"><pre>
Hello
</pre></div>
    </pre></div>
   </div>
   <p class="para">
    It is worth noting that before PHP 5.2.0 the <i>__toString</i>
    method was only called when it was directly combined with
    <a href="function.echo.html" class="function">echo()</a> or <a href="function.print.html" class="function">print()</a>.
    Since PHP 5.2.0, it is called in any string context (e.g. in
    <a href="function.printf.html" class="function">printf()</a> with <i>%s</i> modifier) but not
    in other types contexts (e.g. with <i>%d</i> modifier).
    Since PHP 5.2.0, converting objects without <i>__toString</i>
    method to string would cause <b><tt>E_RECOVERABLE_ERROR</tt></b>.
   </p>
  </div>

  <div id="language.oop5.magic.set-state" class="sect2">
   <h3 class="title"><i>__set_state</i></h3>
   <p class="para">
    This <a href="language.oop5.static.html" class="link">static</a> method is called
    for classes exported by <a href="function.var-export.html" class="function">var_export()</a> since PHP 5.1.0.
   </p>
   <p class="para">
    The only parameter of this method is an array containing exported
    properties in the form <i>array(&#039;property&#039; =&gt; value, ...)</i>.
   </p>
   <div class="example">
    <p><b>Example #3 Using <i>__set_state</i> (since PHP 5.1.0)</b></p>
    <div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB">&lt;?php<br /><br /></span><span style="color: #007700">class&nbsp;</span><span style="color: #0000BB">A<br /></span><span style="color: #007700">{<br />&nbsp;&nbsp;&nbsp;&nbsp;public&nbsp;</span><span style="color: #0000BB">$var1</span><span style="color: #007700">;<br />&nbsp;&nbsp;&nbsp;&nbsp;public&nbsp;</span><span style="color: #0000BB">$var2</span><span style="color: #007700">;<br /><br />&nbsp;&nbsp;&nbsp;&nbsp;public&nbsp;static&nbsp;function&nbsp;</span><span style="color: #0000BB">__set_state</span><span style="color: #007700">(</span><span style="color: #0000BB">$an_array</span><span style="color: #007700">)&nbsp;</span><span style="color: #FF8000">//&nbsp;As&nbsp;of&nbsp;PHP&nbsp;5.1.0<br />&nbsp;&nbsp;&nbsp;&nbsp;</span><span style="color: #007700">{<br />&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span style="color: #0000BB">$obj&nbsp;</span><span style="color: #007700">=&nbsp;new&nbsp;</span><span style="color: #0000BB">A</span><span style="color: #007700">;<br />&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span style="color: #0000BB">$obj</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">var1&nbsp;</span><span style="color: #007700">=&nbsp;</span><span style="color: #0000BB">$an_array</span><span style="color: #007700">[</span><span style="color: #DD0000">'var1'</span><span style="color: #007700">];<br />&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><span style="color: #0000BB">$obj</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">var2&nbsp;</span><span style="color: #007700">=&nbsp;</span><span style="color: #0000BB">$an_array</span><span style="color: #007700">[</span><span style="color: #DD0000">'var2'</span><span style="color: #007700">];<br />&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;return&nbsp;</span><span style="color: #0000BB">$obj</span><span style="color: #007700">;<br />&nbsp;&nbsp;&nbsp;&nbsp;}<br />}<br /><br /></span><span style="color: #0000BB">$a&nbsp;</span><span style="color: #007700">=&nbsp;new&nbsp;</span><span style="color: #0000BB">A</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">$a</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">var1&nbsp;</span><span style="color: #007700">=&nbsp;</span><span style="color: #0000BB">5</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">$a</span><span style="color: #007700">-&gt;</span><span style="color: #0000BB">var2&nbsp;</span><span style="color: #007700">=&nbsp;</span><span style="color: #DD0000">'foo'</span><span style="color: #007700">;<br /><br />eval(</span><span style="color: #DD0000">'$b&nbsp;=&nbsp;'&nbsp;</span><span style="color: #007700">.&nbsp;</span><span style="color: #0000BB">var_export</span><span style="color: #007700">(</span><span style="color: #0000BB">$a</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">true</span><span style="color: #007700">)&nbsp;.&nbsp;</span><span style="color: #DD0000">';'</span><span style="color: #007700">);&nbsp;</span><span style="color: #FF8000">//&nbsp;$b&nbsp;=&nbsp;A::__set_state(array(<br />&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;//&nbsp;&nbsp;&nbsp;&nbsp;'var1'&nbsp;=&gt;&nbsp;5,<br />&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;//&nbsp;&nbsp;&nbsp;&nbsp;'var2'&nbsp;=&gt;&nbsp;'foo',<br />&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;//&nbsp;));<br /></span><span style="color: #0000BB">var_dump</span><span style="color: #007700">(</span><span style="color: #0000BB">$b</span><span style="color: #007700">);<br /><br /></span><span style="color: #0000BB">?&gt;</span>
</span>
</code></div>
    </div>

    <div class="example-contents"><p>The above example will output:</p></div>
    <div class="example-contents"><pre>
<div class="cdata"><pre>
object(A)#2 (2) {
  [&quot;var1&quot;]=&gt;
  int(5)
  [&quot;var2&quot;]=&gt;
  string(3) &quot;foo&quot;
}
</pre></div>
    </pre></div>
   </div>
  </div>
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