在php中如何获取深度未知的多维数组的所有键

function getAllKeys($array) {
    $keys = array();
    
    foreach ($array as $key => $value) {
        $keys[] = $key;
        
        if (is_array($value)) {
            $keys = array_merge($keys, getAllKeys($value));
        }
    }
    
    return $keys;
}

// 示例数组
$array = array(
    'key1' => 'value1',
    'key2' => array(
        'key3' => 'value3',
        'key4' => array(
            'key5' => 'value5',
            'key6' => 'value6'
        )
    )
);

// 获取所有键
$allKeys = getAllKeys($array);

// 打印结果
print_r($allKeys);

Array
(
    [0] => key1
    [1] => key2
    [2] => key3
    [3] => key4
    [4] => key5
    [5] => key6
)