先上代码:
<?php
$pattern='/<img((?!src).)*src[\s]*=[\s]*[\'"](?<src>[^\'"]*)[\'"]/i';
$str = '
<p> <strong>教室传来 朗朗读书声</strong></p>
<center><img id="33924998" title="" border="0" src="../../images/attachement/jpg/site282/20160902/d8cb8a72ca2b19336bc509.JPG" sourcedescription="编辑提供的本地文件" sourcename="本地文件"/></center>
<p> </p>';
preg_match_all($pattern,
$str,
$out);
var_dump($out);
?>
((?!src).)*
匹配 非src的字符串
(?<src>[^\'"]*)
匹配src的值并命名为src子匹配