Why would json_encode return an empty string

Question

I have a simple php structure with 3 nested arrays.

I do not use particular objects and I build myself the arrays with 2 nested loops.

Here is a sample of the var_dump of the array I want to convert to Json.

array (size=2)
  'tram B' => 
    array (size=2)
      0 => 
        array (size=3)
          'name' => string 'Ile Verte' (length=9)
          'distance' => int 298
          'stationID' => int 762
      1 => 
        array (size=3)
          'name' => string 'La Tronche Hôpital' (length=18)
          'distance' => int 425
          'stationID' => int 771
  16 => 
    array (size=4)
      0 => 
        array (size=3)
          'name' => string 'Bastille' (length=8)
          'distance' => int 531
          'stationID' => int 397
      1 => 
        array (size=3)
          'name' => string 'Xavier Jouvin' (length=13)
          'distance' => int 589
          'stationID' => int 438

In another script I have a similar structure and json_encode works fine. So I don't understand why json_encode won't work here.

Edit : there seems to be a problem with the encoding. When mb_detect_encoding returns ASCII, the json_encode works but when it returns UTF8, it doesn't work anymore.

Edit2 : json_last_error() returns JSON_ERROR_UTF8 which means : Malformed UTF-8 characters, possibly incorrectly encoded.

Answer 1

Well after 2 hours of digging (cf Edits)

I found out following :

• In my case it's a encoding problem
• mb_detect_encoding returns probably a faulty response, some strings were probably not UTF-8
• using utf8_encode() on those string solved my problem, but see note below

Here is a recursive function that can force convert to UTF-8 all the strings contained in an array:

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;
}

Use it simply like this:

echo json_encode(utf8ize($data));

Note: utf8_encode() encodes ISO-8859-1 string to UTF-8 as per the docs so if you are unsure of the input encoding iconv() or mb_convert_encoding() may be better options as noted in comments and other solutions.

Answer 2

Matthieu Riegler presented really good solution however I had to slightly modify it to handle objects too:

function utf8ize($d) {
    if (is_array($d)) 
        foreach ($d as $k => $v) 
            $d[$k] = utf8ize($v);

     else if(is_object($d))
        foreach ($d as $k => $v) 
            $d->$k = utf8ize($v);

     else 
        return utf8_encode($d);

    return $d;
}

One more note: json_last_error() may be helpful in debugging json_encode()/json_encode() functions.

Answer 3

For me, the answer to this problem was setting charset=utf8 in my PDO connection.

$dbo = new PDO('mysql:host=localhost;dbname=yourdb;charset=utf8', $username, $password);

Answer 4

Adam Bubela also presented really good solution who helped me solved my problem, and here is the simplified function :

function utf8ize($d)
{ 
    if (is_array($d) || is_object($d))
        foreach ($d as &$v) $v = utf8ize($v);
    else
        return utf8_encode($d);

    return $d;
}

Answer 5

I have exactly the same problem on PHP 5.6. I use Open Server + Nginx on Windows 7. All charsets are set to UTF-8. In theory, according the official documentation, flag

JSON_UNESCAPED_UNICODE

should solve this. Unfortunately this is not my case. I do not know, why. All snippets above do not solve my problem, thus I have found my own implementation. I believe it could help someone. At least, Russian letters pass the test.

function utf8ize($d) {
    if (is_array($d) || is_object($d)) {
        foreach ($d as &$v) $v = utf8ize($v);
    } else {
        $enc   = mb_detect_encoding($d);

        $value = iconv($enc, 'UTF-8', $d);
        return $value;
    }

    return $d;
}

Answer 6

This accepted answer works. But in case you are getting your data from MySQL (as I was) there is an easier way.

Once you open you database, before you query you can set the character set using mysqli as follows:

/* change character set to utf8 | Procedural*/
if (!mysqli_set_charset($link, "utf8")) {
    printf("Error loading character set utf8: %s\n", mysqli_error($link));
    exit();
}

OR

/* change character set to utf8 | Object Oriented*/
if (!$mysqli->set_charset("utf8")) {
        printf("Error loading character set utf8: %s\n", $mysqli->error);
        exit();
 }

LINK: http://php.net/manual/en/mysqli.set-charset.php

Answer 7

I ran into this issue on a server running an older version of PHP (5.2). I was using the JSON_FORCE_OBJECT flag, and apparently that isn't supported until 5.3

So if you're using that flag be sure to check your version!

A workaround appears to be just casting to an object before encoding, like:

json_encode((object)$myvar);

Answer 8

I was getting data from ob_get_clean() and had the same problem, but above solutions don't work for me. In my case solution was this, maybe it will help somebody.

$var = mb_convert_encoding($var, 'UTF-8');

Answer 9

The return of mb_detect_encoding may not be correct:

$data = iconv('UTF-8', 'ISO-8859-1', 'La Tronche Hôpital');
var_dump(
    mb_detect_encoding($data),
    mb_detect_encoding($data, array('ISO-8859-1', 'UTF-8'))
);

Depending on the default detection order, the above may return different results, so the encoding is falsely being reported as UTF-8. (Here's a larger example.)

It is likely that your data is not encoded as UTF-8, so json_encode is returning false. You should look at converting your strings to UTF-8 before JSON-encoding:

$fromEncoding = 'ISO-8859-1'; // This depends on the data

array_walk_recursive($array, function (&$value, $key, $fromEncoding) {
    if (is_string($value)) {
        $value = iconv($fromEncoding, 'UTF-8', $value);
    }
}, $fromEncoding);

Answer 10

Since the output is going to end up as JSON (string) anyway, here is a function that can handle all kind of variable type:

    function utf8ize($arg)
    {
        if (is_array($arg))
            foreach ($arg as $k => $v)
                $arg[$k] = utf8ize($v);
         else if(is_object($arg))
            return utf8ize((array) $arg);
         else
            return utf8_encode(strval($arg));
        return $arg;
    }

This answer is improvement from Matthieu Riegler and Adam Bubela's answer, but this one can handle all type of variable / data type (e.g.: resource like file handle/stream/phpgd/sql connection)

I'm using cast as array when the argument is object in order to prevent error if the object property is read only or private/protected.

Also, on else case, I strval it to handle other data type like resource

I'm using this function to 'force' a variable into string (e.g.: when var_dump-ing or logging to text file)

Answer 11

I have improved Adam Bubela's answer. I just hate it when blocks are not closed by { and }. It's cleaner and you don't introduce bugs or maybe it's that I did use Perl in the past :)

<?php

class App_Updater_String_Util {    
    /**
     * Usage: App_Updater_String_Util::utf8_encode( $data );
     *
     * @param mixed $d
     * @return mixed
     * @see http://stackoverflow.com/questions/19361282/why-would-json-encode-returns-an-empty-string
     */
    public static function utf8_encode($d) {
        if (is_array($d)) {
            foreach ($d as $k => $v) {
                $d[$k] = self::utf8_encode($v);
            }
        } elseif (is_object($d)) {
            foreach ($d as $k => $v) {
                $d->$k = self::utf8_encode($v);
            }
        } elseif (is_scalar($d)) {
            $d = utf8_encode($d);
        }

        return $d;
    }
}

?>

Answer 12

using utf8_encode() on those string solved my problem.

Answer 13

If you get this data from a database, use mysqli_set_charset($connection, "utf8"); in connection when get the params from database

Answer 14

In my case the reason for the API returning an empty JSON was that the properties of the object were set to private.