俩个文件求绝对路径

/**
* 文件找绝对路径
* @param unknown $a
* @param unknown $b */
function getRelativePath($a,$b){
$RelativePath = '';
$pathA = explode('/', dirname($a));
$pathB = explode('/', dirname($b));
$n = 0;
$len = count($pathA)>count($pathB)?count($pathB):count($pathA);
do{
if($n >= $len || $pathA[$n] != $pathB[$n]){
break;
}
}while (++$n);
$RelativePath .= str_repeat('../', count($pathB)-$n);
$RelativePath .= implode('/',array_splice($pathA,$n));
return $RelativePath;
}