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Editorial Team
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Asked: 2026-06-01T11:52:48+00:00

Goal: json_encode a PHP object that has private properties Send the encoded object as

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Goal:

  1. json_encode a PHP object that has private properties
  2. Send the encoded object as a datastring through Low Level AJAX using jQuery
  3. json_decode the PHP object in the AJAX URL to which the request is sent
  4. win

Problem:

On step 3, json_last_error is returning 3 (JSON_ERROR_CTRL_CHAR Control character error, possibly incorrectly encoded)

The Class:

class Stream {
    private $limit;
    private $type;
    private $sort;
    private $offset=0;
    private $userID;
    private $catID;
    private $content = array();
    private $num_posts;

    function __construct(){
        $a = func_get_args();
        $i = func_num_args();
        if (method_exists($this,$f='__construct'.$i)) {
            call_user_func_array(array($this,$f),$a);
        }
    }

    function __construct5($limit, $type, $sort, $userID, $catID){
        $this->limit = $limit;
        $this->type = $type;
        $this->sort = $sort;
        $this->userID = $userID;
        $this->catID = $catID;
        //$this->num_posts = $this->retrieveTotal();

        //$this->setContent(); 
    }

    function __get($name) {
        if(isset($this->$name)){
            return $this->$name;
        }
    }

        public function encodeJSON(){
        foreach ($this as $key => $value){
            if($key != 'content'){
                $json->$key = $value;
            }
        }
        return json_encode($json);
    }

    public function decodeJSON($json_str){
        $json = json_decode($json_str, true);
        echo '<br>error: '.json_last_error();

        foreach ($json as $key => $value){
            $this->$key = $value;
        }
    }
}

//create the object to be encoded
$strm = new Stream(5, 'toc', ' ', 1, ' ');

/*this test works

$d=$strm->encodeJSON();

$st = new Stream();
$st->decodeJSON($d);
*/

The AJAX function:

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js" type="text/javascript"></script>
<script type="text/javascript">
    //load more posts
    $("#active").live("click", function() {
    var stream= '<?= $strm->encodeJSON();?>'; 
        var dataString = 'stream='+stream;
        var request = $.ajax({  
            type: "POST",  
            url: "ajax/loadmore.php",  
            data: dataString,
            beforeSend:function(data){
                $('.load-more').html('<img src="ajax/loader.gif" alt="Loading..." />');
            },
            success: function(html) {
                $('#active').remove();
                $('#stream').append(html);
            }
        });

        //ajax error reporting
        request.fail(function(jqXHR, textStatus) {
            $('#active').html(textStatus);
        });
    });
</script>

<a class='load-more' id='active'>load more posts</a>

The AJAX request (loadmore.php):

require_once'../../classes/stream.class.php';
$strm = new Stream();
$strm->decodeJSON($_POST['stream']);

What I have tried:

This snippet of code

$d=$strm->encodeJSON();

$st = new Stream();
$st->decodeJSON($d);

works fine. That would lead me to believe that AJAX is interfering with the decoding.

I have also tried changing $json = json_decode($json_str, true); to $json = json_decode(utf8_encode($json_str), true); and nothing changes.

NOTE: suggesting that I make the class properties public is NOT a solution

EDIT: when I echo the string, {
"limit": "5",
"type": "toc",
"sort": " ",
"offset": "0",
"userID": "3",
"catID": " ",
"num_posts": "2"
} being sent to decodeJSON it tests as valid

This screenshot shows the arg $json_str that is being sent to decodeJSON($json_str) and the error code.
json_str param and error

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1 Answer

  1. Editorial Team

    After much trial and error I figured out the issue. When I was instantiating the Stream objectthat was to be encoded, instead of using 1 i was using $userID which was being cast as a string and messing with the URI encoding

    stream=%7B%22limit%22%3A%225%22%2C%22type%22%3A%22toc%22%2C%22sort%22%3A%22%20%22%2C%22offset%22%3A%220%22%2C%22userID%22%3A%223%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%22%2C%22catID%22%3A%22%20%22%2C%22num_posts%22%3A%222%22%7D

    I’m not really sure WHY it behaves that way, but the solution is casting the $userID as an integer. so:

    $strm = new Stream(5, 'toc', ' ', (int)$userID, ' ');

    The URI encoding changes to:

    stream=%7B%22limit%22%3A%225%22%2C%22type%22%3A%22toc%22%2C%22sort%22%3A%22%20%22%2C%22offset %22%3A%220%22%2C%22userID%22%3A%223%22%2C%22catID%22%3A%22%20%22%2C%22num_posts%22%3A%222%22%7D

    and json_decode return an array.

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