Add field to a JSON file - php

Question

I have a very simple JSON file "json.txt" :
{
"status": true,
"data":
{
"clics":
[
{
"id": "1",
"title": "Title 1",
"comment": "Blablabla 1",
"url": "http://photostodisplay/1.jpg"
},
{
"id": "2",
"Title": "Title 2",
"comment": "Blablabla 2",
"url": "http://photostodisplay/2.jpg"
}
]
}
}
and I would like to add data and get the following result :
{
"status": true,
"data":
{
"clics":
[
{
"id": "1",
"title": "Title 1",
"comment": "Blablabla 1",
"url": "http://photostodisplay/1.jpg"
},
{
"id": "2",
"Title": "Title 2",
"comment": "Blablabla 2",
"url": "http://photostodisplay/2.jpg"
},
{
"id": "3",
"Title": "Title 3",
"comment": "Blablabla 3",
"url": "http://photostodisplay/3.jpg"
}
]
}
}
The php code I use return the following error :
Fatal error: Cannot use object of type stdClass as array in /home/XXXX/www/clic/test.php on line 10
Here is the php code
<?php
ini_set('display_errors',1);
ini_set('display_startup_errors',1);
error_reporting(-1);
$file = 'json.txt';
$data = json_decode(file_get_contents($file));
$newdata = array('id'=>'11', 'title' => 'sfdfsdfqf', 'comment' => 'sfdfwwfwdsdfqf', 'url' => 'sdfqwsfsdqqfqqqsfcq');
$data[] = $newdata;
file_put_contents($file, json_encode($data));
echo OK
?>
EDIT - Cezary answer gives almost what I need but is not. Here is what I get :
{
"status": true,
"data": {
"clics": [
{
"id": "1",
"title": "Title 1",
"comment": "Blablabla 1",
"url": "http://photostodisplay/1.jpg"
},
{
"id": "2",
"Title": "Title 2",
"comment": "Blablabla 2",
"url": "http://photostodisplay/2.jpg"
}
]
},
"0": {
"id": "11",
"title": "sfdfsdfqf",
"comment": "sfdfwwfwdsdfqf",
"url": "sdfqwsfsdqqfqqqsfcq"
}
}

Answer 1

The issue lies with this bit of code:
$data = json_decode(file_get_contents($file));
This returns an object, not an associative array. Change that line to this:
$data = json_decode(file_get_contents($file), true);
The second argument in json_decode specifies whether you want an associative array or not, and it defaults to false.
EDIT:
You're currently adding something to the root array. To add to the clics array, you can replace $data[] = $newdata; with:
$data['data']['clics'][] = $newdata;

Answer 2

Shouldn't that be
$data["data"]["clics"][]=$newdata;
or
array_push($data["data"]["clics"],$newdata);