PHP函数array_keys

array_keys返回数组的所有键

/**
 * Return all the keys of an array
 * @link https://php.net/manual/en/function.array-keys.php
 * @param array $input <p>
 * An array containing keys to return.
 * </p>
 * @param mixed $search_value [optional] <p>
 * If specified, then only keys containing these values are returned.
 * </p>
 * @param bool $strict [optional] <p>
 * Determines if strict comparison (===) should be used during the search.
 * </p>
 * @return array an array of all the keys in input.
 */
function array_keys(array $input, $search_value = null, $strict = null) { }

 array_keys接受三个参数

• $input 输入的数组
• $search_value 如果指定了，就返回包含指定值的那些键
• $strict 如果为 true，则严格比较。

示例一：

$arr = [
    'name' => 'Rose',
    'age' => 18,
    'addr' => 'CN'
];

var_dump(array_keys($arr));

//结果
//array(3) {
//    [0] =>
//  string(4) "name"
//    [1] =>
//  string(3) "age"
//    [2] =>
//  string(4) "addr"
//}

示例二：传递第二个参数

$arr = [
    'name' => 'Rose',
    'age' => 18,
    'addr' => 'CN'
];

var_dump(array_keys($arr, 'Rose'));

//结果
//array(1) {
//    [0] =>
//  string(4) "name"
//}

示例三：比较第三个参数false和true的区别

$arr = [
    'name' => 'Rose',
    'age' => 18,
    'addr' => 'CN'
];

var_dump(array_keys($arr, '18', false));
//结果
//array(1) {
//    [0] =>
//  string(3) "age"  // 返回键age
//}

//注意区别：
var_dump(array_keys($arr, '18', true));
//结果
//array(0) {
//}