json_decode

(PHP 5 >= 5.2.0, PHP 7, PHP 8, PECL json >= 1.2.0)

json_decode — 对 JSON 格式的字符串进行解码

说明

json_decode(
    string $json,
    ?bool $associative = null,
    int $depth = 512,
    int $flags = 0
): mixed

接受一个 JSON 编码的字符串并且把它转换为 PHP 值。

参数

json

待解码的 json string 格式的字符串。

这个函数仅能处理 UTF-8 编码的数据。

注意:
PHP 实现了 JSON 的一个超集，参考 » RFC 7159.

associative

当为 true 时，JSON 对象将返回关联 array；当为 false 时，JSON 对象将返回 object。当为 null 时，JSON 对象将返回关联 array 或 object，这取决于是否在 flags 中设置 JSON_OBJECT_AS_ARRAY。

depth

需要解码的结构，其最大嵌套深度。该值必须大于 0 或者小于等于 2147483647。

flags

由 JSON_BIGINT_AS_STRING、JSON_INVALID_UTF8_IGNORE、JSON_INVALID_UTF8_SUBSTITUTE、JSON_OBJECT_AS_ARRAY、JSON_THROW_ON_ERROR 组成的掩码。这些常量的行为在 JSON constants 页面有进一步描述。

返回值

返回在 json 中编码的数据作为合适的 PHP 类型。没有引号的值 true、false 和 null 会相应地返回 true、false 和 null。如果 json 无法被解码，或者编码数据深度超过了嵌套限制的话，将会返回 null。

错误／异常

如果 depth 超出允许的范围，自 PHP 8.0.0 起将会抛出 ValueError，在此之前的版本将会引发 E_WARNING 级别的错误。

更新日志

版本	说明
7.3.0	`flags` 新增 `JSON_THROW_ON_ERROR`。
7.2.0	现在 `associative` 允许为 null。
7.2.0	`flags` 新增 `JSON_INVALID_UTF8_IGNORE`、`JSON_INVALID_UTF8_SUBSTITUTE`。
7.1.0	An empty JSON key ("") can be encoded to the empty object property instead of using a key with value `_empty_`.

示例

示例 #1 json_decode() 的例子

<?php
$json = '{"a":1,"b":2,"c":3,"d":4,"e":5}';

var_dump(json_decode($json));
var_dump(json_decode($json, true));

?>

以上示例会输出：

object(stdClass)#1 (5) {
    ["a"] => int(1)
    ["b"] => int(2)
    ["c"] => int(3)
    ["d"] => int(4)
    ["e"] => int(5)
}

array(5) {
    ["a"] => int(1)
    ["b"] => int(2)
    ["c"] => int(3)
    ["d"] => int(4)
    ["e"] => int(5)
}

示例 #2 Accessing invalid object properties

Accessing elements within an object that contain characters not permitted under PHP's naming convention (e.g. the hyphen) can be accomplished by encapsulating the element name within braces and the apostrophe.

<?php

$json = '{"foo-bar": 12345}';

$obj = json_decode($json);
print $obj->{'foo-bar'}; // 12345

?>

示例 #3 common mistakes using json_decode()

<?php

// the following strings are valid JavaScript but not valid JSON

// the name and value must be enclosed in double quotes
// single quotes are not valid 
$bad_json = "{ 'bar': 'baz' }";
json_decode($bad_json); // null

// the name must be enclosed in double quotes
$bad_json = '{ bar: "baz" }';
json_decode($bad_json); // null

// trailing commas are not allowed
$bad_json = '{ bar: "baz", }';
json_decode($bad_json); // null

?>

示例 #4 depth errors

<?php
// Encode some data with a maximum depth  of 4 (array -> array -> array -> string)
$json = json_encode(
    array(
        1 => array(
            'English' => array(
                'One',
                'January'
            ),
            'French' => array(
                'Une',
                'Janvier'
            )
        )
    )
);

// Show the errors for different depths.
var_dump(json_decode($json, true, 4));
echo 'Last error: ', json_last_error_msg(), PHP_EOL, PHP_EOL;

var_dump(json_decode($json, true, 3));
echo 'Last error: ', json_last_error_msg(), PHP_EOL, PHP_EOL;
?>

以上示例会输出：

array(1) {
  [1]=>
  array(2) {
    ["English"]=>
    array(2) {
      [0]=>
      string(3) "One"
      [1]=>
      string(7) "January"
    }
    ["French"]=>
    array(2) {
      [0]=>
      string(3) "Une"
      [1]=>
      string(7) "Janvier"
    }
  }
}
Last error: No error

NULL
Last error: Maximum stack depth exceeded

示例 #5 json_decode() of large integers

<?php
$json = '{"number": 12345678901234567890}';

var_dump(json_decode($json));
var_dump(json_decode($json, false, 512, JSON_BIGINT_AS_STRING));

?>

以上示例会输出：

object(stdClass)#1 (1) {
  ["number"]=>
  float(1.2345678901235E+19)
}
object(stdClass)#1 (1) {
  ["number"]=>
  string(20) "12345678901234567890"
}

注释

注意:
The JSON spec is not JavaScript, but a subset of JavaScript.

注意:
In the event of a failure to decode, json_last_error() can be used to determine the exact nature of the error.

参见

json_encode() - 对变量进行 JSON 编码
json_last_error() - 返回最后发生的错误
json_last_error_msg() - 返回最后一次调用 json_encode() 或 json_decode() 时产生的错误信息

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＋添加备注

用户贡献的备注 5 notes

down

Lennart Hengstmengel ¶

2 years ago

JSON can be decoded to PHP arrays by using the $associative = true option. Be wary that associative arrays in PHP can be a "list" or "object" when converted to/from JSON, depending on the keys (of absence of them). 

You would expect that recoding and re-encoding will always yield the same JSON string, but take this example:

    $json = '{"0": "No", "1": "Yes"}';
    $array = json_decode($json, true);  // decode as associative hash
    print json_encode($array) . PHP_EOL;

This will output a different JSON string than the original:

    ["No","Yes"]

The object has turned into an array!

Similarly, a array that doesn't have consecutive zero based numerical indexes, will be encoded to a JSON object instead of a list.

    $array = [
        'first',
        'second',
        'third',
    ];
    print json_encode($array) . PHP_EOL;
    // remove the second element
    unset($array[1]);
    print json_encode($array) . PHP_EOL;

The output will be:

    ["first","second","third"]
    {"0":"first","2":"third"}

The array has turned into an object! 

In other words, decoding/encoding to/from PHP arrays is not always symmetrical, or might not always return what you expect!

On the other hand, decoding/encoding from/to stdClass objects (the default) is always symmetrical. 

Arrays may be somewhat easier to work with/transform than objects. But especially if you need to decode, and re-encode json, it might be prudent to decode to objects and not arrays. 

If you want to enforce an array to encode to a JSON list (all array keys will be discarded), use:

    json_encode(array_values($array));

If you want to enforce an array to encode to a JSON object, use:

    json_encode((object)$array);

See also: https://www.php.net/manual/en/function.array-is-list.php

down

cubefox at web dot NOSPAMPLEASE dot de ¶

4 years ago

Warning: As the section "return values" mentions, the return value NULL is ambiguos. To repeat, it can mean three things:

* The input string had the value "null"
* There was an error while parsing the input data
* The encoded data was deeper than the recursion limit

To distinguish these cases, json_last_error() can be used.

down

greaties at ghvernuft dot nl ¶

1 year ago

To load an object with data in json format:
(bugfixed my previous comment)

<?php
function loadJSON($Obj, $json)
{
    $dcod = json_decode($json);
    $prop = get_object_vars ( $dcod );
    foreach($prop as $key => $lock)
    {
        if(property_exists ( $Obj ,  $key ))
        {
            if(is_object($dcod->$key))
            {
                loadJSON($Obj->$key, json_encode($dcod->$key));
            }
            else
            {
                $Obj->$key = $dcod->$key;
            }
        }
    }
    return $Obj;
}
?>

Tested with: 

<?php
class Name
{
  public $first;
  public $last;
  public function fullname()
  {
    return $this->first . " " . $this->last;
  }
}
$json = '{"first":"John","last":"Smith"}';

$infull = loadJSON((new Name), $json);
echo $infull->fullname();

down

Alien426 ¶

3 years ago

Browsers don't choke on integers _starting_ with BigInt (64 bits), but before that (53 bits). The introduction of BigInt to modern browsers doesn't help much, when JSON handling functions do not support it. So I am trying to remedy that. My approach is to handle the decoded array before re-encoding it to a string:
<?php
function fix_large_int(&$value)
 {
  if (is_int($value) && $value > 9007199254740991)
    $value = strval($value);
 }
$json_str = '{"id":[1234567890123456789,12345678901234567890]}';
$json_arr = json_decode($json_str, flags: JSON_BIGINT_AS_STRING | JSON_OBJECT_AS_ARRAY);
echo(json_encode($json_arr)); // {"id":[1234567890123456789,"12345678901234567890"]} (BigInt is already converted to a string here)
array_walk_recursive($json_arr, 'fix_large_int');
echo(json_encode($json_arr)); // {"id":["1234567890123456789","12345678901234567890"]}
?>

down

pablo dot pazos at cabolabs dot com ¶

1 month ago

The return value says "Returns the value encoded in json as an appropriate PHP type.", that seems to be the description for the json_encode.