PHP key_exists

此函数同array_key_exsits().

1.函数的作用：判断一个数组是否含有某个键值

2.函数的参数：

　　@param string  $key

　　@param array $haystack

3.

例子一：

<?php
$arr = ['key' => null];

echo "To check whether key exist?
";
echo "The result of the isset() function : " .( isset($arr['key']) ? 1 : 0 )."
";
echo "The result of the key_exists() function :" .key_exists('key',$arr) ."
";
echo "It's a big problem! The isset() function is faster than the key_exists() function.
";
echo "So you can use the snip code :
";

if(isset($arr['key']) || key_exists('key',$arr)){
    echo "'Key' is exist in arr array!
";
}

例子二：