php preg_match_all combined with str_replace replaces all img in the content

There are a lot of javascript scripts and useless information in the collected image img tags. You must replace what you want, such as alt. First look at the content to be filtered, I copied it casually:

sdfsdfsdf<img alt=”3568df.com靓图” src=”http://www.aaa.com/upimg /080330/120D1232295023X0.gif” src=”http://www.eee.com/upimg/080330 /120D1232295023X0.gif” width=1 onclick=”javascript:; ” onload=”javascript:if(this.width>500){this.resized=true; this.style.width=500;}”>sfsdfsdfasdfsadf<img alt=”3568df.com靓图 ” src=”http://www.3568.com/upimg/080330 /120D1232295023X0.gif” src=”http://www.ddd.com/upimg/080330 /120D1232295023X0.gif” width=1 onclick=”javascript:; ” onload=”javascript:if(this.width>500){this.resized=true; this.style.width=500;}”>sdfsadf<img alt=”3568df.com靓图 ” src=”http://www.xxx.com/upimg/080330/120D1232295023X0.gif” src=”http://www.sss.com/upimg/080330/120D1232295023X0.gif” width=1 onclick=”javascript:;” onload=”javascript:if(this.width>500){this.resized=true;this.style.width=500;}”>sdfsdf

To replace the above into the form:

<img alt=”我的信息” src=”http://www.xxx.com/upimg /080330/120D1232295023X0.gif” src=”http://www.xxx.com/upimg/080330 /120D1232295023X0.gif” /> 其中src=”http://www.xxx.com/upimg/080330 /120D1232295023X0.gif” src=”http://www.xxx.com/upimg/080330 /120D1232295023X0.gif”这个地址要保留，因为图片用的都是源地址

The method is roughly: first read all the IMG tags in the content, and then The SRC of each IMG tag is extracted, combined into its own content, and finally replaced.
preg_match_all is the function I want. It can create a three-dimensional array of the content matched by the regular expression. You can traverse them to find and replace them. If you don’t know much about it, please check the manual. I won’t introduce it in detail here. Function code:

function replace($str) 
{ 
preg_match_all(”/<img(.*)(src=\”[^\"]+\”)[^>]+>/isU”, $str, $arr); 
for($i=0,$j=count($arr[0]);$i<$j;$i++){ 
$str = str_replace($arr[0][$i],”<img alt=\”我的信息” “.$arr[2][$i].” />”,$str); 
} 
return $str; 
}

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