json decode - jak funguje?

{
    "appnews": {
        "appid": 440,
        "newsitems": [
            {
                "gid": "521612247017608543",
                "title": "Team Fortress 2 Update Released",
                "url": "http://store.steampowered.com/news/externalpost/tf2_blog/521612247017608543",
                "is_external_url": true,
                "author": "",
                "contents": "An update to Team Fortress 2 has been released. The update will be applied automatically when you restart Team Fortress 2. The major changes include: * Fixed a problem that was preventing clients from uploading items to the Steam Workshop ",
                "feedlabel": "TF2 Blog",
                "date": 1410386700,
                "feedname": "tf2_blog"
            },
            {
                "gid": "521612247017428766",
                "title": "Team Fortress 2 Update Released",
                "url": "http://store.steampowered.com/news/14354/",
                "is_external_url": false,
                "author": "Valve",
                "contents": "An update to Team Fortress 2 has been released. The update will be applied automatically when you restart Team Fortress 2. The major changes include: * Fixed a problem that was preventing clients from uploading items to the Steam Workshop; ",
                "feedlabel": "Product Update",
                "date": 1410386700,
                "feedname": "steam_updates"
            },
            {
                "gid": "521612247015463937",
                "title": "Team Fortress 2 Update Released",
                "url": "http://store.steampowered.com/news/externalpost/tf2_blog/521612247015463937",
                "is_external_url": true,
                "author": "",
                "contents": "An update to Team Fortress 2 has been released. The update will be applied automatically when you restart Team Fortress 2. The major changes include: * Added taunts to the items that can be uploaded to the Steam Workshop ;* Added new \"Taunt\" and \"Halloween\" tags to the Steam Workshop; * Previous ent...",
                "feedlabel": "TF2 Blog",
                "date": 1410382620,
                "feedname": "tf2_blog"
            }
        ]
        
    }
}

$obj = json_decode($json);
print $obj->{'gid'}; 

Notice: Undefined property: stdClass::$gid in *\json.php on line