PHP Cannot Access Empty Element only when input is 0

Question

I am brand new to PHP and I thought my code was working but there seems to be a slight bug.

This is my code:

<?php

    $string = file_get_contents("jsontest.txt");
    $result = json_decode($string);

    if(isset($_POST['value']) && !empty($_POST['value']) &&
         isset($_POST['whatElement']) && !empty($_POST['whatElement']) &&
         isset($_POST['category']) && !empty($_POST['category']) &&
         isset($_POST['model']) && !empty($_POST['model'])) {

        $value = $_POST['value'];
        $whatElement = $_POST['whatElement'];
        $category = $_POST['category'];
        $model = $_POST['model'];
  }


  $result->$category->$model->$whatElement = $value;
  echo $result->$category->$model->$whatElement;

  $myfile = fopen("jsontest.txt", "w") or die("Unable to open file!");
    $txt = json_encode($result);
    fwrite($myfile, $txt);
?>

I was using this as a response to an HTML input tag. If it is relevant this is the javascript code that I use to call my PHP script

function handleEnter(value, type, exactModel)
{
    var bothParts = exactModel.split("_");
    category = bothParts[0];
    model = bothParts[1];

    $.ajax({
        url: "morework.php",
        data: {value: value, whatElement: type, category: category, model: model},
        type: 'post',
        success: function(ret){
            //location.reload();
            console.log(ret);
        }
    })

}

This passes the proper data to the PHP script but when the "value" variable is set as 0 I get the following: "Fatal error: Cannot access empty property in..."

I have tried to change the code as follows:

Instead of: $result->$category->$model->$whatElement = $value;

I put: $result->category->model->whatElement = $value;

This seems to handle the error but does not change the json file at all. Whereas if I had the original it does not work for 0 but does change the json file for all other numbers.

I have used var_dump on $_POST and in all cases this seems to hold the correct values. However if I do send in a 0 if I echo this line: echo "$value $whatElement $category $model"; it shows up as empty whereas it is populated when non-zero

Example of the var_dump for a 0 value test:

array(4) {
  ["value"]=>
  string(1) "0"
  ["whatElement"]=>
  string(8) "Borrowed"
  ["category"]=>
  string(9) "Category"
  ["model"]=>
  string(8) "Model"
}

An explanation as to what is happening/advice on how to remedy this is greatly appreciated.

[Why check both isset() and !empty()](https://stackoverflow.com/q/4559925/476) — deceze, Jul 26 '17 at 20:37
Does this answer imply that using !empty() can lead to unwanted results? Or does it serve a purpose? There seems to be conflicting opinions in the answer of the post you have linked. — Abdall, Jul 26 '17 at 20:47
The purpose of `empty` is to do the same check as `== false` *without throwing any errors if the variable you're checking isn't set.* That's it. Nothing more, nothing less. — deceze, Jul 26 '17 at 20:49

Omi · Accepted Answer · 2017-07-26T20:54:12.663

1

The following things are considered to be empty (php manual):

"" (an empty string)
0 (0 as an integer)
0.0 (0 as a float)
"0" (0 as a string)
NULL
FALSE
array() (an empty array)
$var; (a variable declared, but without a value)

So your conition will fail when you have 0 value. You can remove isset($_POST['value']) && !empty($_POST['value']) this from condition. Write this before if condition

if your php version is 7.0 or greater use

 $value =  $_POST['value'] ?? 0;

if php version less than 7.0 use

 $value = isset($_POST['value']) && !empty($_POST['value']) ? $_POST['value']:0;

edited Jul 26 '17 at 20:54

answered Jul 26 '17 at 20:35

Omi

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Thank you for this quick and correct solution. As I am a total beginner can you explain what was happening? Was the if-statement failing? – Abdall Jul 26 '17 at 20:39
1

yes 0 means empty so your condition was failing when you have 0 as value – Omi Jul 26 '17 at 20:41
You should probably just be using `isset($_POST['value']) ? $_POST['value'] : 0`. In PHP 7, that can be shortened to `$_POST['value'] ?? 0`. Or arguably you should entirely reject the request with an HTTP 400 error if required arguments aren't sent. – deceze Jul 26 '17 at 20:50

PHP Cannot Access Empty Element only when input is 0

1 Answers1