php学习：array->判断值在数组中是否存在

1.php 中的数组底层实现是hashtable，参见http://www.laruence.com/2009/08/23/1065.html

因而要区别key/索引，跟value的区别

2.判断KEY是否存在：array_key_exists(key,array)，http://www.w3school.com.cn/php/func_array_key_exists.asp

<?php
$a=array("a"=>"Dog","b"=>"Cat");
if (array_key_exists("a",$a))
	{
	echo "Key exists!";
	}
else
	{
	echo "Key does not exist!";
	}
?>

输出为：

Key exists!

3.判断value是否存在：in_array(value,array,type)，http://www.w3school.com.cn/php/func_array_in_array.asp

<?php
$people = array("Peter", "Joe", "Glenn", "Cleveland");

if (in_array("Glenn",$people))
  {
  echo "Match found";
  }
else
  {
  echo "Match not found";
  }
?>

输出为：

Match found