php有什么鲜为人知的技巧？

一些大家很少用，却很方便的函数等？

回复内容：

没事上来水一下。

1、cal_days_in_month(calendar,month,year)
作用：
针对指定的年份和日历，返回一个月中的天数。
参数：
calendar 必需。规定要使用的历法。
month 必须。规定月。
year 必须。规定年。
栗子：

<code class="language-php"><span class="cp"><?php </span>
<span class="nv">$days</span> <span class="o">=</span> <span class="nb">cal_days_in_month</span><span class="p">(</span><span class="nx">CAL_GREGORIAN</span><span class="p">,</span><span class="mi">10</span><span class="p">,</span><span class="mi">2015</span><span class="p">);</span>
<span class="k">echo</span> <span class="s2">"There was </span><span class="si">$days</span><span class="s2"> days in October 2015"</span><span class="p">;</span>
<span class="cp">?></span><span class="x"></span>
</span></code>

可变变量 PHP: 可变变量

<code class="language-text"><?php //You can even add more Dollar Signs

  $Bar = "a";
  $Foo = "Bar";
  $World = "Foo";
  $Hello = "World";
  $a = "Hello";

  $a; //Returns Hello
  $$a; //Returns World
  $$$a; //Returns Foo
  $$$$a; //Returns Bar
  $$$$$a; //Returns a

  $$$$$$a; //Returns Hello
  $$$$$$$a; //Returns World

  //... and so on ...//

?>
</code>