PHP - json_decode() of a JSON string is null

Question

I'm calling this line in my browser:

example.com/save.php?params={"objID":"i8O0FRuGEr","username":"johndoe","password":123456,"email":"[email protected]","followedBy":["john","sarah"]}

and here's my save.php code:

<?php 
include 'Config.php';

    $getJSON = $_GET['params'];
    echo 'getJSON: '.$getJSON.'<br><br>';

    $updateArr = json_decode($getJSON, true);
    echo 'UPDATE_ARR: ' .$updateArr; //<-- it prints 'null'...

    $jsonStr = file_get_contents("Users.json");
    // Decode the JSON string into a PHP array.
    $objects = json_decode($jsonStr, true);

    array_push($objects, $updateArr);

    // Encode the array back into a JSON string and save it.
    $jsonData = json_encode($objects);
    file_put_contents("Users.json", $jsonData);

    // echo data
    echo 'JSON DATA: ' .$jsonData;
?>

The problem is this code makes my User.json file 'null', it removes all objects in it, in fact, the echo 'UPDATE_ARR: ' .$updateArr; returns null. I would need to decode my $getJSON string into a PHP array, as I do for my User.json file (the $jsonStr), but it doesn't work.

What am I doing wrong?

Thanks so much!

You can use json_last_error() to determine the exact nature of the error. php.net/manual/en/function.json-last-error.php — beingalex
– beingalex, Commented Sep 12, 2018 at 14:20

Gufran Hasan · Accepted Answer · 2018-09-12 15:33:33Z

1

I have updated your code and tested at my side it's working now. Please try it.

  <?php 
    include 'Config.php'; 
     if(!empty($_GET['params'])){
    $getJSON = $_GET['params'];
    echo 'getJSON: '.$getJSON.'<br><br>';

    $updateArr = json_decode($getJSON, true);
    echo 'UPDATE_ARR: ';print_r($updateArr); //<-- it prints 'null'...

    $jsonStr = file_get_contents("Users.json");
    // Decode the JSON string into a PHP array.
    $objects = json_decode($jsonStr, true);

    array_push($objects, $updateArr);

    // Encode the array back into a JSON string and save it.
    $jsonData = json_encode($objects);
    file_put_contents("Users.json", $jsonData);

    // echo data
    echo 'JSON DATA: ' .$jsonData;
}else{
    echo 'Params is empty';
}

This is the outcome of users.json file after refreshing many times:

getJSON: {"objID":"i8O0FRuGEr","username":"johndoe","password":123456,"email":"[email protected]","followedBy":["john","sarah"]} UPDATE_ARR: Array ( [objID] => i8O0FRuGEr [username] => johndoe [password] => 123456 [email] => [email protected] [followedBy] => Array ( [0] => john [1] => sarah ) ) JSON DATA: {"ID":"i8O0FRuGEr","user_name":"johndoe","pass":123456,"email_id":"[email protected]","followed_By":["john","sarah"],"0":{"objID":"i8O0FRuGEr","username":"johndoe","password":123456,"email":"[email protected]","followedBy":["john","sarah"]},"1":null,"2":{"objID":"i8O0FRuGEr","username":"johndoe","password":123456,"email":"[email protected]","followedBy":["john","sarah"]},"3":{"objID":"i8O0FRuGEr","username":"johndoe","password":123456,"email":"[email protected]","followedBy":["john","sarah"]},"4":{"objID":"i8O0FRuGEr","username":"johndoe","password":123456,"email":"[email protected]","followedBy":["john","sarah"]},"5":{"objID":"i8O0FRuGEr","username":"johndoe","password":123456,"email":"[email protected]","followedBy":["john","sarah"]},"6":{"objID":"i8O0FRuGEr","username":"johndoe","password":123456,"email":"[email protected]","followedBy":["john","sarah"]},"7":{"objID":"i8O0FRuGEr","username":"johndoe","password":123456,"email":"[email protected]","followedBy":["john","sarah"]},"8":{"objID":"i8O0FRuGEr","username":"johndoe","password":123456,"email":"[email protected]","followedBy":["john","sarah"]}}

After using your users.json file:

[{"objID":"i8O0FRuGEr","username":"johndoe","password":123456,"email":"[email protected]","followedBy":["john","sarah"]},{"objID":"i8O0FRuGEr","username":"johndoe","password":123456,"email":"[email protected]","followedBy":["john","sarah"]},{"objID":"i8O0FRuGEr","username":"johndoe","password":123456,"email":"[email protected]","followedBy":["john","sarah"]},{"objID":"i8O0FRuGEr","username":"johndoe","password":123456,"email":"[email protected]","followedBy":["john","sarah"]},{"objID":"i8O0FRuGEr","username":"johndoe","password":123456,"email":"[email protected]","followedBy":["john","sarah"]}]

edited Sep 12, 2018 at 15:33

answered Sep 12, 2018 at 14:16

Gufran Hasan

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12 Comments

Frank Eno Over a year ago

oh, so it was a matter of wrong echoing :) thanks so much, it works now!

Gufran Hasan Over a year ago

Yes, you were trying to echo array as a string .$updateArr;

Frank Eno Over a year ago

i don’t know why but it still adds a null object in my User.json file.»

Gufran Hasan Over a year ago

The same code as I updated? Let me check it again at my side.

Gufran Hasan Over a year ago

Yes, it's adding null second time. The reason is that it adds null for duplicate data.

|

Kumar Sree · Accepted Answer · 2018-09-12 14:04:16Z

1

It seems $getJson is null.

check its value using var_dump function or print_r function.

var_dump($getJson); // see what is the output.

answered Sep 12, 2018 at 14:04

Kumar Sree

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Comments

Martin Zeitler · Accepted Answer · 2018-09-12 14:09:19Z

1

this is no JSON string, while you won't properly urlencode() the query-string. die(urlencode('{"objID":"i8O0FRuGEr","username":"johndoe","password":123456,"email":"[email protected]","followedBy":["john","sarah"]}'));

^ append the above PHP output as params=.

rather proper would be, to POST the JSON as the content.

edited Sep 12, 2018 at 14:09

answered Sep 12, 2018 at 14:03

Martin Zeitler

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Comments

Eriks Klotins · Accepted Answer · 2018-09-12 14:17:11Z

1

PHP documentation states that json_decode() returns NULL if the string cannot be decoded. Most likely it is a syntax error originating from bad url encoding.

Why are you json encoding url parameters in the first place? URL encoding is the accepted way to pass params in urls.

EDIT:

print_r($updateArr);

Shows a correct json, thus the problem is elsewhere

There are several other issues with your code.

echo 'UPDATE_ARR: ' .$updateArr; throws Notice: Array to string conversion on line 6. Depending on your PHP version and configuration, your NULL could be printed because of bad typecasting in echo.
Warning: array_push() expects parameter 1 to be array, null given on line 12. Check if your users.json file exists and is correct.

edited Sep 12, 2018 at 14:17

answered Sep 12, 2018 at 14:05

Eriks Klotins

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