$a = ['aa', 'bb', 'cc'];
$ret = json_encode($a);
var_dump($ret);

$a = [ 'a' => 'aa', 'b' => 'bb', 'c' => 'cc'];
$ret = json_encode($a);
var_dump($ret);

$a = [ 0 => 'aa', 1 => 'bb', 2 => 'cc'];
$ret = json_encode($a);
var_dump($ret);

$a = [ 2 => 'aa', 3 => 'bb', 4 => 'cc'];
$ret = json_encode($a);
var_dump($ret);

$a = ['aa', 'bb', 'cc'];
$ret = json_encode($a, JSON_FORCE_OBJECT);
var_dump($ret); 

$ret = (object)$a; // 强制将php数组变成了php对象
var_dump($ret); 
$ret = json_encode($ret); // 将php对象转换成json对象
var_dump($ret);

$str = '{"name":"zhangsan", "age": 18}';
$ret2 = json_decode($str, true);
var_dump($ret2);

$str = '["q", "w", "e"]';
$ret = json_decode($str, true);
var_dump($ret);

array(2) {
 ["name"]=>
 string(8) "zhangsan"
 ["age"]=>
 int(18)
}
array(3) {
 [0]=>
 string(1) "q"
 [1]=>
 string(1) "w"
 [2]=>
 string(1) "e"
}

$str = '{"name":"zhangsan", "age": 18}';
$ret = json_decode($str);
var_dump($ret);

var_dump($ret->name);

object(stdClass)#1 (2) {
 ["name"]=>
 string(8) "zhangsan"
 ["age"]=>
 int(18)
}
string(8) "zhangsan"

class TestJson {
    const CONST_VALUE_A = 'aaa';
    public $b = 'bbb';
    protected $c = 'ccc';
    private $d = 'ddd';
    public function hello() {

        print_r("hello\n");
    }
    public static $stValue = 'st';

}

$test = new TestJson();
var_dump($ret);
$ret = json_encode($test);
var_dump($ret);

// 存数据
$raw = file_get_contents('php://input');
$param = json_decode($raw, true);
var_dump($param);
$s = json_encode($param);
var_dump($s); 

……
// 将$s存到了数据库表对应字段里面
……
……

// 取数据
$column = json_deocde($c, true);
$resp = [
 'status' => 0,
 'column' => $column,
];
echo json_encode($resp);

// 取数据
$column = json_deocde($c, true);
if (empty($column)) {
 $column = (object)$column; // 强制将php空数组变成了php对象
}
$resp = [
 'status' => 0,
 'column' => $column,
];
echo json_encode($resp);