php 函数中静态变量使用的问题实例分析

<?php
function msg() {
  static $a = 0;
  echo $a++, '<br />';
}

msg();
msg();
msg();

$data = array(
  array('id' => 1, 'title' => '衣服', 'parent' => 0),
  array('id' => 2, 'title' => '鞋子', 'parent' => 0),
  array('id' => 3, 'title' => '衬衫', 'parent' => 1),
  array('id' => 4, 'title' => 't恤', 'parent' => 1),
  array('id' => 5, 'title' => '运动鞋', 'parent' => 2),
  array('id' => 6, 'title' => '休闲鞋', 'parent' => 2),
);

$data2 = array(
  array('id' => 1, 'title' => '食物', 'parent' => 0),
  array('id' => 2, 'title' => '肉食', 'parent' => 1),
  array('id' => 3, 'title' => '素食', 'parent' => 1),
  array('id' => 4, 'title' => '牛肉', 'parent' => 2),
  array('id' => 5, 'title' => '面条', 'parent' => 3),
  array('id' => 6, 'title' => '馒头', 'parent' => 3),
);

//生成树型数据
function gentree($items, $id = 'id', $pid = 'parent', $son = 'child') {
  $tree = array();
  $tmpmap = array();

  foreach ($items as $item) {
    $tmpmap[$item[$id]] = $item;
  }
  foreach ($items as $item) {
    if (isset($tmpmap[$item[$pid]])) {
      $tmpmap[$item[$pid]][$son][] = &$tmpmap[$item[$id]];
    } else {
      $tree[] = &$tmpmap[$item[$id]];
    }
  }
  unset($tmpmap);
  return $tree;
}

//通过给定数据，返回option的字符串，用于select下拉框
function getopts($data, $idarr = array(), $level = 0, $son = 'child') {
  static $opt = '';
  if (!empty($data)) {
    foreach ($data as $k => $v) {
      $opt .= '<option value=' . $v['id'] . (in_array($v['id'], $idarr) ? ' selected="true"' : '') . '>' . str_repeat(' ', $level * 3) . $v['title'] . '</option>';
      if (!empty($v[$son])) {
        getopts($v[$son], $idarr, $level + 1, $son);
      }
    }
  }
  return $opt;
}

$data = gentree($data);
echo '<select>';
//第一次调用getopts时，没有任何问题。
echo getopts($data);
echo '</select>';

$data2 = gentree($data2);
echo '<select>';
//当第二次调用时，问题就出现了，还留有上次的数据
echo getopts($data2);
echo '</select>';

function getopts($data, $idarr = array(), &$opt = '', $level = 0, $son = 'child') {
  if (!empty($data)) {
    foreach ($data as $k => $v) {
      $opt .= '<option value=' . $v['id'] . (in_array($v['id'], $idarr) ? ' selected="true"' : '') . '>' . str_repeat(' ', $level * 3) . $v['title'] . '</option>';
      if (!empty($v[$son])) {
        getopts($v[$son], $idarr, $opt, $level + 1, $son);
      }
    }
  }
}

$data = gentree($data);
getopts($data, array(), $opt);
echo '<select>';
echo $opt;
echo '</select>';

$data2 = gentree($data2);
getopts($data2, array(), $opt2);
echo '<select>';
echo $opt2;
echo '</select>';