Cannot read NULL variable in PHP after posting JSON array through .ajax()

Question

I'm having a problem like many other people, being able to read a PHP array variable after having sent it through ajax() post. Ajax is succeeding and displaying the returned data, which is NULL. I have already thoroughly researched SO solutions for this JSON/PHP problem, and my problem description shows 'almost' EVERY solution on SO so far.

On the PHP side I've tried:

$data = json_decode(file_get_contents('php://input'), true);
var_dump($data);

(Skipping over $HTTP_RAW_POST_DATA (deprecated) because it's equal to file_get_contents('php://input')

and also:

$data = json_decode($_POST["a_arr"], true);

I've already tried clearing the UTF-8 BOM with the sed command

sed '1s/^\xEF\xBB\xBF//' < index.html > index2.html

My .ajax() looks like this:

$.ajax ({
    url:"file.php",
    method:"post",
    contentType: "application/json; charset=utf-8",
    data: { a_arr : JSON.stringify(arr) },
    })
    .done(function(response){
        $("#status").html(response);
    });

On the Javascript side here is my array:

var arr = [{"name":_name, "phone":_phone, "email":_email, "repname":repname, "repnumber":repnumber, "office":office}];
ajax_post(arr);

I've checked to make sure there is no JSON formatting error, the following successfully shows me a valid JSON formatted array:

var data_arr = JSON.stringify(arr);
document.getElementById("status").innerHTML = data_arr;

Possible duplicate of How can I use JQuery to post JSON data? — miken32
– miken32, Commented May 17, 2019 at 20:28
I have thoroughly reviewed SO for similar JSON/PHP cases, and though while close in appearance, I have found no solution as my problem description illustrates. — user3285269
– user3285269, Commented May 20, 2019 at 15:35

Barmar · Accepted Answer · 2019-05-17 20:00:00Z

1

You need to change to:

data: JSON.stringify(arr),

When you give an object to the data: option, it converts it to URL-encoded format, not JSON.

Or you can leave the data: option as it is, but get rid of the contentType: option, and then you should use

$data = json_decode($_POST['a_arr'], true);

answered May 17, 2019 at 20:00

Barmar

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6 Comments

user3285269 Over a year ago

Very grateful for the input and information! Ok, I tried your suggesttion, relying on data: to push URL encoding, I removed the name and put: data: JSON.stringify(arr), This also returns NULL! Then I put the data: element back to JSON format: data: { a_arr : JSON.stringify(arr) }, Commented out the contentType: //contentType: "application/json; charset=utf-8", And lastly switched from php://input over to: $data = json_decode($_POST['a_arr'], true); $var_dump($data); is still NULL in both cases :(

Barmar Over a year ago

What version of jQuery are you using? The method: option was added in 1.9.0, before that it was type:.

Barmar Over a year ago

What do you see in var_dump(file_get_contents("php://input"));?

user3285269 Over a year ago

Using: jquery-1.8.3.min.js

user3285269 Over a year ago

Wow, nice suggestion: the return data is: string(0) "" Which is funny because I get a valid javascript JSON string pre .ajax()

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