如何在PHP中从关联数组创建嵌套Json数组

<?php
// 创建一个关联数组
$data = array(
    'name' => 'John Doe',
    'age' => 30,
    'email' => 'johndoe@example.com',
    'address' => array(
        'street' => '123 Main St',
        'city' => 'New York',
        'state' => 'NY',
        'country' => 'USA'
    )
);

// 将关联数组转换为JSON字符串
$json = json_encode($data);

// 输出JSON字符串
echo $json;
?>

{
    "name": "John Doe",
    "age": 30,
    "email": "johndoe@example.com",
    "address": {
        "street": "123 Main St",
        "city": "New York",
        "state": "NY",
        "country": "USA"
    }
}