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 ';