How to convert php null values to null in JSON string?

Question

I have a system that sends and receives all data as JSON strings, and therefore must format all the data I need to send to it as a JSON string.

I am receiving values from a form using a PHP POST call, then using these values to create a string in a JSON format. The problem is with NULL values as well as true and false values. When these values are included in the string from the POST values it simply leaves it blank, but the JSON formats a NULL value as the text null.

See the example below:

<?php

$null_value = null;
$json_string = '{"uid":0123465,"name":"John Smith","nullValue":'.$null_value.'}';
echo $json_string;

//output
{"uid":0123465,"name":"John Smith","nullValue":} 

?>

However, the correct output I need is:

$json_string = '{"uid":0123465,"name":"John Smith","nullValue":null}';
echo $json_string;

//output
{"uid":0123465,"name":"John Smith","nullValue":null} 

?>

My question is, how can I get PHP null values to appear correctly as JSON null values, rather than just leaving it empty? Is there a method for converting them?

Laurynas Mališauskas · Accepted Answer · 2013-08-19 10:36:51Z

2

do not create your JSON string by hand. PHP has an excellent function http://php.net/manual/en/function.json-encode.php

answered Aug 19, 2013 at 10:36

Laurynas Mališauskas

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2 Comments

denoise Over a year ago

but what if someone wants to add extra data to the JSON string? json_encode wouldn't be a viable option.

Laurynas Mališauskas Over a year ago

@denoise decode the string, add new values and encode to get the new JSON string

deceze · Accepted Answer · 2013-08-19 10:37:35Z

1

Don't manually cobble JSON together!

$data = array('uid' => '0123465', 'name' => 'John Smith', 'nullValue' => null);
$json = json_encode($data);

answered Aug 19, 2013 at 10:37

deceze♦

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2 Comments

Daniele Salvatore Albano Over a year ago

Well, there are situations where using json_encode isn't feasable and encoding it "manually" let you to stream it while extracting datas

deceze Over a year ago

Agreed. But then one should know what one is doing. ;) I'd also still use json_encode to encode individual values or sub-objects with the correct syntax.

MaveRick · Accepted Answer · 2013-08-19 10:38:55Z

1

you can do some check:

$null_value = null;
if(strlen($null_value) < 1)
    $null_value = 'null';//quote 'null' so php deal with this var as a string NOT as null value
$json_string = '{"uid":0123465,"name":"John Smith","nullValue":'.$null_value.'}';
echo $json_string;

or you can quote the value null at the beginning:

$null_value = 'null';
$json_string = '{"uid":0123465,"name":"John Smith","nullValue":'.$null_value.'}';
echo $json_string;

but the prefered way to do it is to collect values in an array then encode it:

$null_value = null;
$json_string = array("uid"=>0123465,"name"=>"John Smith","nullValue"=>$null_value);
echo json_encode($json_string,JSON_FORCE_OBJECT);

answered Aug 19, 2013 at 10:38

MaveRick

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1 Comment

Kyle Dearle Over a year ago

The problem with doing $null_value = 'null', is that it turns the value into a string, and the receiver is not expecting a string value which then returns an error. But the json_encode is correct, not sure why I forgot about this method. Thank you for the comprehensive answer.

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