PHP-返回产生奇怪结果的变量

我遇到了一个奇怪的问题，即echo'ing变量正在工作，而$str.=正在产生奇怪的结果

    function displayComments($comments, $str){
        foreach ($comments as $info) {
            $str .= $info['id'];
            if (!empty($info['childs'])) {
                $this->displayComments($info['childs'],$str);
            }
        }
        return $str;
       }

     $comments = $this->produceComments($id);
            if(!$comments){
                $str ='
                    <tr>
                        <td>There are no comments for this Project</td>
                    </tr>';
            }else{
                $str = $this->displayComments($comments,'');        
            }

echo $str;

接下来，我尝试使用$str.=构建并响应函数

function displayComments($comments,$str=FALSE){
    foreach ($comments as $info) {
        $str .= $info['id'];
        if (!empty($info['childs'])) {
            $this->displayComments($info['childs']);
        }
    }
    echo $str;
    return $str;
  }

这会产生5,6,4,1,2,3，这是不正常和奇怪的。。当它在函数外回声时，它产生1，2，3 为什么正确地回显$info['id']输出，但将值构建到$str中不起作用，同时返回$str会删除值

还有，为什么在函数内部使用$str进行echo’ing会在函数内部产生不同的组合，而不是在返回后在函数外部产生不同的组合

阵列

Array
   (
       [1] => Array
           (
               [0] => 1
               [id] => 1
               [1] => 1
               [project_id] => 1
               [2] => 0
              [parent] => 0
              [3] => First post
              [comment] => First post
              [4] => 
              [user] => 
              [5] => 2014-02-01
              [date] => 2014-02-01
              [childs] => Array
                  (
                  )

          )

      [2] => Array
          (
              [0] => 2
              [id] => 2
              [1] => 1
              [project_id] => 1
              [2] => 0
              [parent] => 0
              [3] => Second Post
              [comment] => Second Post
              [4] => 
              [user] => 
              [5] => 2014-02-01
              [date] => 2014-02-01
              [childs] => Array
                  (
                      [0] => Array
                          (
                              [0] => 5
                              [id] => 5
                              [1] => 1
                              [project_id] => 1
                              [2] => 2
                              [parent] => 2
                              [3] => Reply to 2nd post
                              [comment] => Reply to 2nd post
                              [4] => 
                              [user] => 
                              [5] => 2014-02-05
                              [date] => 2014-02-05
                              [childs] => Array
                                  (
                                  )

                          )

                      [1] => Array
                          (
                              [0] => 6
                              [id] => 6
                              [1] => 1
                              [project_id] => 1
                              [2] => 2
                              [parent] => 2
                              [3] => Reply to 2nd post
                              [comment] => Reply to 2nd post
                              [4] => 
                              [user] => 
                              [5] => 2014-02-05
                              [date] => 2014-02-05
                              [childs] => Array
                                  (
                                  )

                          )

                  )

          )

      [3] => Array
          (
              [0] => 3
              [id] => 3
              [1] => 1
              [project_id] => 1
              [2] => 0
              [parent] => 0
              [3] => Reply to first post
              [comment] => Reply to first post
              [4] => 
              [user] => 
              [5] => 2014-02-19
              [date] => 2014-02-19
              [childs] => Array
                  (
                      [0] => Array
                         (
                             [0] => 4
                             [id] => 4
                             [1] => 1
                             [project_id] => 1
                             [2] => 3
                             [parent] => 3
                             [3] => Reply to first reply
                             [comment] => Reply to first reply
                             [4] => 
                             [user] => 
                             [5] => 2014-02-05
                             [date] => 2014-02-05
                             [childs] => Array
                                 (
                                 )

                         )

                 )

         )

 )

我很肯定

foreach ($comments as $info) {
        $str .= $info['id'];
        if (!empty($info['childs'])) {
            $this->displayComments($info['childs'],$str);
        }
    }

应该是

foreach ($comments as $info) {
        $str .= $info['id'];
        if (!empty($info['childs'])) {
            $str = $this->displayComments($info['childs'],$str);
        }
    }

---

您使用的是递归，但一旦您真正递归，您就不会对返回数据做任何事情，因此它似乎从未发生过。

当我看到这一点时，我也是这么想的。如果要构建$str字符串，请在被调用的方法之外定义它，并且只附加到它。在第一个例子中，有一个“$str=”可能导致了这种奇怪的行为。这正是问题所在。非常感谢，戴夫。

foreach ($comments as $info) {
        $str .= $info['id'];
        if (!empty($info['childs'])) {
            $str = $this->displayComments($info['childs'],$str);
        }
    }