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

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 2

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 3

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 4

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

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

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;
}