# json_decode

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

json_decode — 对 JSON 格式的字符串进行解码

### 说明

json_decode ( string `$json` [, bool `$assoc` = false [, int `$depth` = 512 [, int `$options` = 0 ]]] ) : mixed

接受一个 JSON 编码的字符串并且把它转换为 PHP 变量

### 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。

  > Note:

  > PHP implements a superset of JSON as specified in the original » RFC 7159.

`assoc`

  当该参数为 `TRUE` 时，将返回 array 而非 object 。

`depth`

  指定递归深度。

`options`

  JSON解码的掩码选项。 现在有两个支持的选项。 第一个是`JSON_BIGINT_AS_STRING`， 用于将大整数转为字符串而非默认的float类型。第二个是 `JSON_OBJECT_AS_ARRAY`， 与将`assoc`设置为 `TRUE` 有相同的效果。

### 返回值

Returns the value encoded in `json` in appropriate PHP type. Values true, false and null are returned as `TRUE`, `FALSE` and `NULL` respectively. `NULL` is returned if the `json` cannot be decoded or if the encoded data is deeper than the recursion limit.

### 范例

Example #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)
    }

Example #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

    ?>

Example #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

    ?>

Example #4 `depth` errors

    <?php
    // Encode the data.
    $json = json_encode(
        array(
            1 => array(
                'English' => array(
                    'One',
                    'January'
                ),
                'French' => array(
                    'Une',
                    'Janvier'
                )
            )
        )
    );

    // Define the errors.
    $constants = get_defined_constants(true);
    $json_errors = array();
    foreach ($constants["json"] as $name => $value) {
        if (!strncmp($name, "JSON_ERROR_", 11)) {
            $json_errors[$value] = $name;
        }
    }

    // Show the errors for different depths.
    foreach (range(4, 3, -1) as $depth) {
        var_dump(json_decode($json, true, $depth));
        echo 'Last error: ', $json_errors[json_last_error()], PHP_EOL, PHP_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: JSON_ERROR_NONE

    NULL
    Last error: JSON_ERROR_DEPTH

Example #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));

    ?>

以上例程会输出：

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

### 注释

> Note:

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

> Note:

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

### 更新日志

版本 | 说明
--- | ---
7.1.0 | An empty JSON key ("") can be encoded to the empty object property instead of using a key with value _empty_.
7.0.0 | Rejected RFC 7159 incompatible number formats - top level (07, 0xff, .1, -.1) and all levels ([1.], [1.e1])
7.0.0 | An empty PHP string or value that after casting to string is an empty string (NULL, FALSE) results in JSON syntax error.
5.6.0 | Invalid non-lowercased variants of the true, false and null literals are no longer accepted as valid input, and will generate warnings.
5.4.0 | The `options` parameter was added.
5.3.0 | Added the optional `depth`. The default recursion depth was increased from 128 to 512
5.2.3 | The nesting limit was increased from 20 to 128
5.2.1 | Added support for JSON decoding of basic types.

### 参见

- json_encode() - 对变量进行 JSON 编码
- json_last_error() - 返回最后发生的错误