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根据一个文件的路径来计算另一个文件的相对路径

2017-02-28 17:56 Posted in Learn with PHP

这是另一道在PHP面试的时候经常考到的题目，解决思路也比较直接。

首先将两个路径都破开成为数组，然后对比相同的部分，这里有个需要注意的点：找相同部分的时候不能使用array_intersect，因为类似

	$path1 = '/home/web/lib/img/cache.php';    
	$path2 = '/home/web/api/img/show.php';

这样的路径就会解析错误,因为array_intersect会把两个数组中相同的元素全部提取出来，导致后面我们根据路径有多少相同部分来添加..定位符的时候就会出BUG。

代码如下：

<?php  
/**
* calculate relative path from $from to $to, both need to be absolute path
* @param $from string from path
* @param $to string to path
* @return string relative path to $to
*/
function getRelativePath($from, $to){  
    $fromArr = explode(DIRECTORY_SEPARATOR, $from);
    //remove file's basename
    array_shift($fromArr);
    //remove the first empty element
    array_pop($fromArr);
    $toArr = explode(DIRECTORY_SEPARATOR, $to);
    array_shift($toArr);
    
    $inter = [];
    for ($i = 0; $i < count($fromArr); $i++)
    {
    	if ($fromArr[$i] === $toArr[$i])
    	{
    		array_push($inter, $fromArr[$i]);
    	}
    	else
    	{
    		break;
    	}
    }
	
	$diff = array_diff($fromArr, $inter);
	
	//$from and $to are in same directory
	if (! $diff)
	{
		$prefix = ['.'];
	}
	else
	//how many same parts that these files path contain, we add that many '..' locator
	{
		$prefix = array_fill(0, count($diff), '..');
	}
	
	$toArr = array_slice($toArr, count($inter));
	
	$relativeTo = array_merge($prefix, $toArr);
	
	$relativeTo = implode(DIRECTORY_SEPARATOR, $relativeTo);
	
	return $relativeTo;
}