PHP:从数组获取密钥？

$array = array('key1' => 'value1', 'key2' => 'value2', 'key3' => 'value3');
$key = 'key2';
$value = $array[$key];
echo $value; // 输出：value2

$array = array('key1' => 'value1', 'key2' => 'value2', 'key3' => 'value3');
$keys = array_keys($array);
$key = $keys[1];
echo $key; // 输出：key2

$array = array('key1' => 'value1', 'key2' => 'value2', 'key3' => 'value3');
foreach ($array as $key => $value) {
    echo "Key: $key, Value: $value\n";
}