字符匹配的有关问题

$str = '请问怎么在一堆源码中匹配以下字符

img id="main-image" src="http://ecx.images-mazon.com/images/I/41Auzc7RBPL._SY300_.jpg"';



$p = '#img\s*id="main-image"\s*src="(http://ecx\.images-mazon\.com/images/I/.+\.(jpg
------解决方案--------------------
gif
------解决方案--------------------
jpeg
------解决方案--------------------
png))"#U';

preg_match($p, $str, $result) && var_dump($result);

$html = '
';

$doc = new DOMDocument();

$doc->loadHTML($html);

echo $doc->getElementById('main-image')->getAttribute('src');

$str='img id="main-image" src="http://ecx.images-mazon.com/images/I/41Auzc7RBPL._SY300_.jpg"';

$p = 
------解决方案--------------------
img id="main-image" src="//m.sbmmt.com/m/faq/(.*)"
------解决方案--------------------
iUs;

preg_match($p, $str, $result);

print_r($result);

//如果你只需要对获取到的网址里那个图片名称那么你需要分割

$ep=explode('//m.sbmmt.com/m/',$result[0]);

echo $ep[5];