json_last_error()

(PHP 5 >= 5.3.0, PHP 7)

返回最后发生的错误

说明

json_last_error(void): int

如果有，返回 JSON 编码解码时最后发生的错误。

参数

此函数没有参数。

返回值

返回一个整型（integer），这个值会是以下的常量之一：

范例

json_last_error()例子

<?php
// 一个有效的 json 字符串
$json[] = '{"Organization": "PHP Documentation Team"}';
// 一个无效的 json 字符串会导致一个语法错误，在这个例子里我们使用 ' 代替了 " 作为引号
$json[] = "{'Organization': 'PHP Documentation Team'}";
foreach ($json as $string) {
    echo 'Decoding: ' . $string;
    json_decode($string);
    switch (json_last_error()) {
        case JSON_ERROR_NONE:
            echo ' - No errors';
        break;
        case JSON_ERROR_DEPTH:
            echo ' - Maximum stack depth exceeded';
        break;
        case JSON_ERROR_STATE_MISMATCH:
            echo ' - Underflow or the modes mismatch';
        break;
        case JSON_ERROR_CTRL_CHAR:
            echo ' - Unexpected control character found';
        break;
        case JSON_ERROR_SYNTAX:
            echo ' - Syntax error, malformed JSON';
        break;
        case JSON_ERROR_UTF8:
            echo ' - Malformed UTF-8 characters, possibly incorrectly encoded';
        break;
        default:
            echo ' - Unknown error';
        break;
    }
    echo PHP_EOL;
}
?>

以上例程会输出：

Decoding: {"Organization": "PHP Documentation Team"} - No errors
Decoding: {'Organization': 'PHP Documentation Team'} - Syntax error, malformed JSON

json_encode()的json_last_error()

<?php
// 无效的 UTF8 序列
$text = "\xB1\x31";
$json  = json_encode($text);
$error = json_last_error();
var_dump($json, $error === JSON_ERROR_UTF8);
?>

以上例程会输出：

string(4) "null"
bool(true)

参见

• json_last_error_msg()Returns the error string of the last json_encode()or json_decode()call
• json_decode()对 JSON 格式的字符串进行解码
• json_encode()对变量进行 JSON 编码

While this can obviously change between versions, the current error codes are as follows:
0 = JSON_ERROR_NONE
1 = JSON_ERROR_DEPTH
2 = JSON_ERROR_STATE_MISMATCH
3 = JSON_ERROR_CTRL_CHAR
4 = JSON_ERROR_SYNTAX
5 = JSON_ERROR_UTF8
I'm only posting these for people who may be trying to understand why specific JSON files are not being decoded. Please do not hard-code these numbers into an error handler routine.

use this code with mb_convert_encoding, you can json_encode some corrupt UTF-8 chars
  function safe_json_encode($value, $options = 0, $depth = 512) {
    $encoded = json_encode($value, $options, $depth);
    if ($encoded === false && $value && json_last_error() == JSON_ERROR_UTF8) {
      $encoded = json_encode(utf8ize($value), $options, $depth);
    }
    return $encoded;
  }
  function utf8ize($mixed) {
    if (is_array($mixed)) {
      foreach ($mixed as $key => $value) {
        $mixed[$key] = utf8ize($value);
      }
    } elseif (is_string($mixed)) {
      return mb_convert_encoding($mixed, "UTF-8", "UTF-8");
    }
    return $mixed;
  }

I used this simple script, flicked from StackOverflow to escape from the function failing:
<?php
  function utf8ize($d) {
    if (is_array($d)) {
      foreach ($d as $k => $v) {
        $d[$k] = utf8ize($v);
      }
    } else if (is_string ($d)) {
      return utf8_encode($d);
    }
    return $d;
  }
?>
Cheers,
Praveen Kumar!

when json_decode a empty string, PHP7 will trigger an Syntax error:
<?php
json_decode("");
var_dump(json_last_error(), json_last_error_msg());
// PHP 7
int(4)
string(12) "Syntax error"
// PHP 5
int(0)
string(8) "No error"

Just adding this note since I had to code this for the actual values reference.
<?php
echo JSON_ERROR_NONE . ' JSON_ERROR_NONE' . '<br />';
echo JSON_ERROR_DEPTH . ' JSON_ERROR_DEPTH' . '<br />';
echo JSON_ERROR_STATE_MISMATCH . ' JSON_ERROR_STATE_MISMATCH' . '<br />';
echo JSON_ERROR_CTRL_CHAR . ' JSON_ERROR_CTRL_CHAR' . '<br />';
echo JSON_ERROR_SYNTAX . ' JSON_ERROR_SYNTAX' . '<br />';
echo JSON_ERROR_UTF8 . ' JSON_ERROR_UTF8' . '<br />';
echo JSON_ERROR_RECURSION . ' JSON_ERROR_RECURSION' . '<br />';
echo JSON_ERROR_INF_OR_NAN . ' JSON_ERROR_INF_OR_NAN' . '<br />';
echo JSON_ERROR_UNSUPPORTED_TYPE . ' JSON_ERROR_UNSUPPORTED_TYPE' . '<br />';
/*
The above outputs :
0 JSON_ERROR_NONE
1 JSON_ERROR_DEPTH
2 JSON_ERROR_STATE_MISMATCH
3 JSON_ERROR_CTRL_CHAR
4 JSON_ERROR_SYNTAX
5 JSON_ERROR_UTF8
6 JSON_ERROR_RECURSION
7 JSON_ERROR_INF_OR_NAN
8 JSON_ERROR_UNSUPPORTED_TYPE
*/
?>

here is a small updated version of utf8ize that has the following addition : 
* It uses iconv instead of utf8_encode for potentially better result.
* It adds the support of objects variable 
* It also update array key value (in a case I met I had to utf8ize the key as well as those were generated from a user input value)
Here is the code.
<?php
  function utf8ize($d) {
    if (is_array($d)) {
      foreach ($d as $k => $v) {
        unset($d[$k]);
    $d[utf8ize($k)] = utf8ize($v);
      }
    } else if (is_object($d)) {
    $objVars = get_object_vars($d);
    foreach($objVars as $key => $value) {
    $d->$key = utf8ize($value);
    }    
  } else if (is_string ($d)) {
      return iconv('UTF-8', 'UTF-8//IGNORE', utf8_encode($d));
    } 
    return $d;
  }
?>

This is a quite simple and functional trick to validate JSON's strings.
<?php
  function json_validate($string) {
    if (is_string($string)) {
      @json_decode($string);
      return (json_last_error() === JSON_ERROR_NONE);
    }
    return false;
  }
  echo (json_validate('{"test": "valid JSON"}') ? "It's a JSON" : "NOT is a JSON"); // prints 'It's a JSON'
  echo (json_validate('{test: valid JSON}') ? "It's a JSON" : "NOT is a JSON"); // prints 'NOT is a JSON' due to missing quotes
  echo (json_validate(array()) ? "It's a JSON" : "NOT is a JSON"); // prints 'NOT is a JSON' due to a non-string argument
?>
Cheers