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：
1 <?php 2 $arr = ['key' => null]; 3 4 echo "To check whether key exist?\n"; 5 echo "The result of the isset() function : " .( isset($arr['key']) ? 1 : 0 )."\n"; 6 echo "The result of the key_exists() function :" .key_exists('key',$arr) ."\n"; 7 echo "It's a big problem! The isset() function is faster than the key_exists() function.\n"; 8 echo "So you can use the snip code :\n"; 9 10 if(isset($arr['key']) || key_exists('key',$arr)){ 11 echo "'Key' is exist in arr array!\n"; 12 }
例子二：