php query file extension

<span style="color: #008080;"> 1</span> <span style="color: #008000;">//</span><span style="color: #008000;">查询文件扩展名</span>
<span style="color: #008080;"> 2</span> <span style="color: #0000ff;">function</span> extension(<span style="color: #800080;">$str</span><span style="color: #000000;">){
</span><span style="color: #008080;"> 3</span>     <span style="color: #800080;">$str</span> = <span style="color: #008080;">implode</span>("",<span style="color: #008080;">explode</span>("\\",<span style="color: #800080;">$str</span><span style="color: #000000;">));
</span><span style="color: #008080;"> 4</span>     <span style="color: #800080;">$str</span> = <span style="color: #008080;">explode</span>(".",<span style="color: #800080;">$str</span><span style="color: #000000;">);
</span><span style="color: #008080;"> 5</span>     <span style="color: #800080;">$str</span> = <span style="color: #008080;">strtolower</span>(<span style="color: #008080;">end</span>(<span style="color: #800080;">$str</span><span style="color: #000000;">));
</span><span style="color: #008080;"> 6</span>     <span style="color: #0000ff;">return</span> <span style="color: #800080;">$str</span><span style="color: #000000;">;
</span><span style="color: #008080;"> 7</span> <span style="color: #000000;">}
</span><span style="color: #008080;"> 8</span> 
<span style="color: #008080;"> 9</span> <span style="color: #800080;">$file</span> = 'D://a\b\name-Of_somefile.File.txt'<span style="color: #000000;">;
</span><span style="color: #008080;">10</span> <span style="color: #0000ff;">echo</span> extension(<span style="color: #800080;">$file</span>);