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

例子一：

 1 <?php
 2 $arr = ['key' => null];
 3 
 4 echo "To check whether key exist?
";
 5 echo "The result of the isset() function : " .( isset($arr['key']) ? 1 : 0 )."
";
 6 echo "The result of the key_exists() function :" .key_exists('key',$arr) ."
";
 7 echo "It's a big problem! The isset() function is faster than the key_exists() function.
";
 8 echo "So you can use the snip code :
";
 9 
10 if(isset($arr['key']) || key_exists('key',$arr)){
11     echo "'Key' is exist in arr array!
";
12 }

例子二：

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