文件夹递归：何时返回？

问题描述：

What I am trying to do is recursively iterate through all the folders and gathering an $arr from each file that I will later merge. In high level terms this is what I am doing:

function main(){
    $path = ....
    $arr = array();
    if(is_dir($path)){
       $arr = parseFolder($path, $arr);
    } else {
       $arr = parseFile($path);
    }
    print $arr;
}
function parseFile($path){
   ....
   return $arr
}

function parseFolder($path, $arr){
   $folder = opendir($path);
   while($item=readdir($folder)){
      if(is_dir($item)
          parseFolder($path . '/' . $item, $arr);
      else
          $arr = merge_array($arr, parseFile($path . '/' . $item);

   }
   return $arr
}

As you can see there is going to be a problem with this because I don't have a base case. So, it will eventually return $arr multiple times in the parseFolder function. Is there anyway to know when I'm virtually done iterating through all files/folders, so I know when to return my final result $arr? I'm open to more efficient implementations.

我要做的是递归遍历所有文件夹并从每个文件中收集$ arr我将以后合并。在高级术语中，这就是我正在做的事情： p>

  function main（）{
 $ path = .... 
 $ arr = array（  ）; 
 if（is_dir（$ path））{
 $ arr = parseFolder（$ path，$ arr）; 
} else {
 $ arr = parseFile（$ path）; 
} 
 print $  arr; 
} 
 
函数parseFile（$ path）{
 .... 
返回$ arr 
} 
 
函数parseFolder（$ path，$ arr）{
 $ folder = opendir（$ path）  ; 
 while（$ item = readdir（$ folder））{
 if（is_dir（$ item）
 parseFolder（$ path。'/'。$ item，$ arr）; 
 else 
 $ arr =  merge_array（$ arr，parseFile（$ path。'/'。$ item）; 
 
} 
返回$ arr 
} 
  code>  pre> 
 
 当你 可以看出这会有问题，因为我没有基本情况。所以，它最终会在parseFolder函数中多次返回$ arr。无论如何都知道什么时候 我几乎完成了迭代所有文件/文件夹，所以我知道什么时候返回我的最终结果$ arr？ 我愿意接受更有效的实施。 p> 
  div>

答

You need to replace:

parseFolder($path . '/' . $item, $arr);

With

$arr = array_merge($arr, parseFolder($path . '/' . $item, $arr));

Otherwise all of your recursive calls will be thrown away.

Also, I don't think you have a full grasp on recursion as it seems that you think if you return at any point down deep in the recursion it will break all the way back out to the original call. This is incorrect.

The only caveats with recursive functions are:

Make sure you don't infinitely recurse, eg. in this case a symlink to a parent directory.
A sufficiently deep recursion can cause a stack overflow and crash your program.

For #1 you can simply avoid processing symlinks, or to cover both you can implement a depth limit. eg:

<?php
define('RECURSE_MAXDEPTH', 10);

function myRecurse($path, $depth=0) {
  $arr = array();
  $folder = opendir($path);
  while( $item = readdir($folder) ) {
    if( is_dir($item) ) {
      if( $depth < RECURSE_MAXDEPTH ) {
        $arr = array_merge($arr, myRecurse($path.'/'.$item, $depth+1));
      }
    } else {
      $arr = array_merge($arr, someFunction($item));
    }
  }
  return $arr;
}

$myArr = myRecurse('~sammitch/');

答

There are some syntax errors in you code. Missing parenthesis several places, you used constant folder instead of variable $folder and I expect merge_array actually is array_merge?

Your solution seems to be a mix of two approaches:

Mutating version where the supplied reference is added to.

function parseFolder($path, &$arr)
{
    $folder = opendir($path);
    while($item=readdir($folder)) {
        // current and parent directory shouldn't be processed
        if( $item == '.' || $item == '..' )
            continue;
        elseif( is_dir($item) )
            parseFolder($path . '/' . $item, $arr);
        else
            $arr = array_merge($arr, parseFile($path . '/' . $item));
    }
    // the supplied array is updated with the result
}

A version that uses the return value of deeper recursion and build by value.

function parseFolder($path)
{
    $arr = array();
    $folder = opendir($path);
    while($item=readdir($folder)) {
        // current and parent directory shouldn't be processed
        if( $item == '.' || $item == '..' ) 
            continue;
        elseif( is_dir($item) )
            $arr = array_merge($arr, parseFolder($path . '/' . $item));
        else
            $arr = array_merge($arr, parseFile($path . '/' . $item));
    }
    return $arr;
}

文件夹递归：何时返回？

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