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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 arrayobject,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

JSON_BIGINT_AS_STRINGJSON_INVALID_UTF8_IGNOREJSON_INVALID_UTF8_SUBSTITUTEJSON_OBJECT_AS_ARRAYJSON_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

通过恰当的 PHP 类型返回在 json 中编码的数据。值 truefalsenull 会相应地返回 truefalsenull。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_IGNOREJSON_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_.

范例

示例 #1 json_decode() 的例子

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

var_dump(json_decode($json));
var_dump(json_decode($jsontrue));

?>

以上例程会输出:

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(
        
=> array(
            
'English' => array(
                
'One',
                
'January'
            
),
            
'French' => array(
                
'Une',
                
'Janvier'
            
)
        )
    )
);

// Show the errors for different depths.
var_dump(json_decode($jsontrue4));
echo 
'Last error: 'json_last_error_msg(), PHP_EOLPHP_EOL;

var_dump(json_decode($jsontrue3));
echo 
'Last error: 'json_last_error_msg(), PHP_EOLPHP_EOL;
?>

以上例程会输出:

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($json));
var_dump(json_decode($jsonfalse512JSON_BIGINT_AS_STRING));

?>

以上例程会输出:

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

add a note

User Contributed Notes 7 notes

up
8
Lennart Hengstmengel
10 months 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
up
6
Alien426
1 year 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"]}
?>
up
1
cubefox at web dot NOSPAMPLEASE dot de
2 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.
up
-7
greaties at ghvernuft dot nl
1 year ago
To load an object with data in json format:

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;
            }
        }
    }
}
up
-5
as-works at narod dot ru
1 year ago
On some PHP7+ systems php_json functions can be undefined (i faced it on Oracle Linux Enterprice with php 7.4 installed from REMI repository). If you have the same problem, try to install separated php-json module:

# yum install php-json

Hope this helps.
up
-10
Anonymous
1 year ago
<?php

$array
= [0 => "foo", 1 => "bar", 2 => ["baz"]];

$associative = false;

var_dump(
   
json_decode(
       
json_encode($array),
       
$associative
   
)
);

?>

The above will output
<?php
/*
array (size=3)
  0 => string 'foo' (length=3)
  1 => string 'bar' (length=3)
  2 =>
    array (size=1)
      0 => string 'baz' (length=3)
*/
?>

Considering <?php $associative = false; ?> one might expect
<?php
/*
object(stdClass)
  public '0' => string 'foo' (length=3)
  public '1' => string 'bar' (length=3)
  public '2' =>
    object(stdClass)
      public '0' => string 'baz' (length=3)
*/
?>

an stdClass object instead of an array, but this is incorrect.
json_decode will always return an array for a sequentially encoded array, regardless of the ?bool $associative 2nd argument

Which is inline with the above mentioned docs/spec
    > Returns the value encoded in json in appropriate PHP type

Considering that the 1st arg was a sequentially encoded array as a json string
    '["foo","bar",["baz"]]'
up
-23
mattia
1 year ago
if you're using ajax to post, and your JavaScript code looks like this:

<code>
    var xhttp = new XMLHttpRequest();
    xhttp.open("POST", "something.php", true);
    xhttp.setRequestHeader("Content-Type", "application/json");
    xhttp.onreadystatechange = function() {
        if (this.readyState == 4 && this.status == 200) {
             // do something
        }
    };
    var data = {some: "thing"};
    xhttp.send(JSON.stringify(data));
</code>

then in <code>something.php</code> you can retrieve your json by doing

<?php
$data
= json_decode(file_get_contents("php://input"), true);
?>
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