php替换一次

function replace_once($replace,$str,$targetstr)/$replace为要替换的字串，$targetstr为替换字串，$str为原字串
{
$tempstr = $str;
for (;;)
{
$tempindex = strrpos($tempstr,$replace);
if($tempindex!=false)
{
$tempstr = substr($str,0,$tempindex);
}
else break;
}
$replaceindex = strlen($tempstr);
//echo$replaceindex;
//echo $replaceindex."hao";
$str = substr($str,0,$replaceindex).$targetstr.substr($str,$replaceindex+strlen($replace));
return $str;
}