Nrthugu

This is intended to be a general reference question and answer covering many of the never-ending "How do I access data in my JSON?" questions. It is here to handle the broad basics of decoding JSON in PHP and accessing the results.

I have the JSON:

{

    "type": "donut",

    "name": "Cake",

    "toppings": [

        { "id": "5002", "type": "Glazed" },

        { "id": "5006", "type": "Chocolate with Sprinkles" },

        { "id": "5004", "type": "Maple" }

    ]

}

How do I decode this in PHP and access the resulting data?

Intro

First off you have a string. JSON is not an array, an object, or a data structure. JSON is a text-based serialization format - so a fancy string, but still just a string. Decode it in PHP by using json_decode().

 $data = json_decode($json);

Therein you might find:

• scalars: strings, ints, floats, and bools
  


• 
  nulls (a special type of its own)


• compound types: objects and arrays.

These are the things that can be encoded in JSON. Or more accurately, these are PHP's versions of the things that can be encoded in JSON.

There's nothing special about them. They are not "JSON objects" or "JSON arrays." You've decoded the JSON - you now have basic everyday PHP types.

Objects will be instances of stdClass, a built-in class which is just a generic thing that's not important here.

Accessing object properties

You access the properties of one of these objects the same way you would for the public non-static properties of any other object, e.g. $object->property.

$json = '

{

    "type": "donut",

    "name": "Cake"

}';



$yummy = json_decode($json);



echo $yummy->type; //donut

Accessing array elements

You access the elements of one of these arrays the same way you would for any other array, e.g. $array[0].

$json = '

[

    "Glazed",

    "Chocolate with Sprinkles",

    "Maple"

]';



$toppings = json_decode($json);



echo $toppings[1]; //Chocolate with Sprinkles

Iterate over it with foreach.

foreach ($toppings as $topping) {

    echo $topping, "n";

}

Glazed

Chocolate with Sprinkles

Maple

Or mess about with any of the bazillion built-in array functions.

Accessing nested items

The properties of objects and the elements of arrays might be more objects and/or arrays - you can simply continue to access their properties and members as usual, e.g. $object->array[0]->etc.

$json = '

{

    "type": "donut",

    "name": "Cake",

    "toppings": [

        { "id": "5002", "type": "Glazed" },

        { "id": "5006", "type": "Chocolate with Sprinkles" },

        { "id": "5004", "type": "Maple" }

    ]

}';



$yummy = json_decode($json);



echo $yummy->toppings[2]->id; //5004

Passing true as the second argument to json_decode()

When you do this, instead of objects you'll get associative arrays - arrays with strings for keys. Again you access the elements thereof as usual, e.g. $array['key'].

$json = '

{

    "type": "donut",

    "name": "Cake",

    "toppings": [

        { "id": "5002", "type": "Glazed" },

        { "id": "5006", "type": "Chocolate with Sprinkles" },

        { "id": "5004", "type": "Maple" }

    ]

}';



$yummy = json_decode($json, true);



echo $yummy['toppings'][2]['type']; //Maple

Don't know how the data is structured

Read the documentation for whatever it is you're getting the JSON from.

Look at the JSON - where you see curly brackets {} expect an object, where you see square brackets expect an array.

Hit the decoded data with a print_r():

$json = '

{

    "type": "donut",

    "name": "Cake",

    "toppings": [

        { "id": "5002", "type": "Glazed" },

        { "id": "5006", "type": "Chocolate with Sprinkles" },

        { "id": "5004", "type": "Maple" }

    ]

}';



$yummy = json_decode($json);



print_r($yummy);

and check the output:

stdClass Object

(

    [type] => donut

    [name] => Cake

    [toppings] => Array

        (

            [0] => stdClass Object

                (

                    [id] => 5002

                    [type] => Glazed

                )



            [1] => stdClass Object

                (

                    [id] => 5006

                    [type] => Chocolate with Sprinkles

                )



            [2] => stdClass Object

                (

                    [id] => 5004

                    [type] => Maple

                )



        )



)

It'll tell you where you have objects, where you have arrays, along with the names and values of their members.

If you can only get so far into it before you get lost - go that far and hit that with print_r():

print_r($yummy->toppings[0]);

stdClass Object

(

    [id] => 5002

    [type] => Glazed

)

Break the problem down into pieces that are easier to wrap your head around.

json_decode() returns null

This happens because either:

1. The JSON consists entirely of just that, null.


2. The JSON is invalid - check the result of json_last_error_msg or put it through something like JSONLint.


3. It contains elements nested more than 512 levels deep. This default max depth can be overridden by passing an integer as the third argument to json_decode().

If you need to change the max depth you're probably solving the wrong problem. Find out why you're getting such deeply nested data (e.g. the service you're querying that's generating the JSON has a bug) and get that to not happen.

Object property name contains a special character

Sometimes you'll have an object property name that contains something like a hyphen - or at sign @ which can't be used in a literal identifier. Instead you can use a string literal within curly braces to address it.

$json = '{"@attributes":{"answer":42}}';

$thing = json_decode($json);



echo $thing->{'@attributes'}->answer; //42

If you have an integer as property see: How to access object properties with names like integers? as reference.

Someone put JSON in your JSON

It's ridiculous but it happens - there's JSON encoded as a string within your JSON. Decode, access the string as usual, decode that, and eventually get to what you need.

$json = '

{

    "type": "donut",

    "name": "Cake",

    "toppings": "[{ "type": "Glazed" }, { "type": "Maple" }]"

}';



$yummy = json_decode($json);

$toppings = json_decode($yummy->toppings);



echo $toppings[0]->type; //Glazed

Data doesn't fit in memory

If your JSON is too large for json_decode() to handle at once things start to get tricky. See:

• Processing large JSON files in PHP


• How to properly iterate through a big json file

How to sort it

See: Reference: all basic ways to sort arrays and data in PHP.

You can use json_decode() to convert a json string to a PHP object/array.

Eg.

Input:

$json = '{"a":1,"b":2,"c":3,"d":4,"e":5}';



var_dump(json_decode($json));

var_dump(json_decode($json, true));

Output:

object(stdClass)#1 (5) {

    ["a"] => int(1)

    ["b"] => int(2)

    ["c"] => int(3)

    ["d"] => int(4)

    ["e"] => int(5)

}



array(5) {

    ["a"] => int(1)

    ["b"] => int(2)

    ["c"] => int(3)

    ["d"] => int(4)

    ["e"] => int(5)

}

Few Points to remember:

• 
  json_decode requires the string to be a valid json else it will return NULL.


• In the event of a failure to decode, json_last_error() can be used to determine the exact nature of the error.


• Make sure you pass in utf8 content, or json_decode may error out and just return a NULL value.