Undefined offset ошибка

Notice: Undefined offset

This error means that within your code, there is an array and its keys. But you may be trying to use the key of an array which is not set.

The error can be avoided by using the isset() method. This method will check whether the declared array key has null value or not. If it does it returns false else it returns true for all cases.

This type of error occurs with arrays when we use the key of an array, which is not set.

In the following, given an example, we are displaying the value store in array key 1, but we did not set while declaring array “$colorarray.”

Error Example:

<?php
// Declare an array with key 2, 3, 4, 5
$colorarray = array(2=>'Red',3=>'Green',4=>'Blue',5=>'Yellow');
// Printing the value of array at offset 1.
echo $colorarray[1];
?>

Output:

Notice: Undefined offset: 1 in \index.php on line 5

Here are two ways to deal with such notices.

1. Resolve such notices.
2. Ignore such notices.

Fix Notice: Undefined offset by using isset() Function

Check the value of offset array with function isset(), empty(), and array_key_exists() to check if key exist or not.

Example:

<?php
$colorarray = array(2=>'Red',3=>'Green',4=>'Blue',5=>'Yellow');
// isset() function to check value at offset 1 of array
if(isset($colorarray[1])){echo $colorarray[1];}
// empty() function to check value at offset 1 of array
if(!empty($colorarray[1])){echo $colorarray[1];}
// array_key_exists() of check if key 1 is exist or not
echo array_key_exists(1, $colorarray);
?>

How to Ignore PHP Notice: Undefined offset?

You can ignore this notice by disabling reporting of notice with option error_reporting.

1. Disable Display Notice in php.ini file

Open php.ini file in your favourite editor and search for text “error_reporting” the default value is E_ALL. You can change it to E_ALL & ~E_NOTICE.

By default:

error_reporting = E_ALL

Change it to:

error_reporting = E_ALL & ~E_NOTICE

Now your PHP compiler will show all errors except ‘Notice.’

2. Disable Display Notice in PHP Code

If you don’t have access to make changes in the php.ini file, In this case, you need to disable the notice by adding the following code on the top of your php page.

<?php error_reporting (E_ALL ^ E_NOTICE); ?>

Now your PHP compiler will show all errors except ‘Notice.’

Before discovering how to avoid the PHP undefined offset error, let’s see what it is. The undefined offset is the one that doesn’t exist inside an array. An attempt to access such an index will lead to an error, which is known as undefined offset error.

Let’s see an example:

<?php

// Declare and initialize an array
// $students = ['Ann', 'Jennifer', 'Mary']
$students = [
    0 => 'Ann',
    1 => 'Jennifer',
    2 => 'Mary',
];

// Leyla
echo $students[0];

// ERROR: Undefined offset: 5
echo $students[5];

// ERROR: Undefined index: key
echo $students[key];

?>

Below, we will show you several methods to avoid the undefined offset error.

This function allows checking if the variable is set and is not null.

The example of using the isset function to avoid undefined offset error is as follows:

<?php

// Declare and initialize an array
// $students = ['Ann', 'Jennifer', 'Mary']
$students = [
    0 => 'Ann',
    1 => 'Jennifer',
    2 => 'Mary',
];

if (isset($students[5])) {
    echo $students[5];
} else {
    echo "Index not present";
}

?>

Index not present

The empty() function is used for checking if the variable or the index value inside an array is empty.

Here is an example:

<?php

// Declare and initialize an array
// $students = ['Rohan', 'Arjun', 'Niharika']
$students = [
  0 => 'Ann',
  1 => 'Jennifer',
  2 => 'Mary',
];

if (!empty($students[5])) {
  echo $students[5];
} else {
  echo "Index not present";
}

?>

Index not present

This function is used for associative arrays that store data in the key-value pair form, and there is a value for each key.

The array_key_exists function is used for testing if a particular key exists in an array or not.

Here is an example:

<?php
// PHP program to illustrate the use
// of array_key_exists() function

function Exists($index, $array)
{
    if (array_key_exists($index, $array)) {
        echo "Key Found";
    } else {
        echo "Key not Found";
    }
}

$array = [
    "john" => 25,
    "david" => 10,
    "jack" => 20,
];

$index = "jack";

print_r(Exists($index, $array));

?>

Key Found

This is a PHP tutorial on how to “fix” undefined index and undefined offset errors.

These are some of the most common notices that a beginner PHP developer will come across. However, there are two simple ways to avoid them.

What is an index?

Firstly, you will need to understand what an index is.

When you add an element to array, PHP will automatically map that element to an index number.

For example, if you add an element to an empty array, PHP will give it the index “0“. If you add another element after that, it will be given the index “1“.

This index acts as an identifier that allows you to interact with the element in question. Without array indexes, we would be unable to keep track of which element is which.

Take the following array as an example.

//Example array
$animals = array(
    0 => 'Cat',
    1 => 'Dog',
    2 => 'Bird'
);

As you can see, Cat has the index “0” and Dog has the index “1“. If I want to print the word “Cat” out onto the page, I will need to access the “Cat” element via its array index.

//We know that "Cat" is at index 0.
echo $animals[0]; //Prints out "Cat"

As you can see, we were able to access the “Cat” element by specifying the index “0“.

Similarly, if we want to print out the word “Dog”, then we can access it via the index “1“.

//Print out "Dog"
echo $animals[1];

If we want to delete the “Dog” element from our PHP array, then we can do the following.

//Deleting "Dog" from our array.
unset($animals[1]);

The unset function will remove the element in question. This means that it will no longer exist.

An undefined offset notice will occur if you attempt to access an index that does not exist.

This is where you’ll encounter nasty errors such as the following.

Notice: Undefined offset: 1 in /path/to/file.php on line 2

Or, if you are using array keys instead of numerical indexes.

Notice: Undefined index: test in /path/to/file.php on line 2

PHP will display these notices if you attempt to access an array index that does not exist.

Although it is not a fatal error and the execution of your script will continue, these kind of notices tend to cause bugs that can lead to other issues.

$_POST, $_GET and $_SESSION.

A lot of beginner PHP developers fail to realize that $_POST, $_GET, $_SESSION, $_FILES, $_COOKIE, $_SERVER and $_REQUEST are all predefined arrays.

These are what we call superglobal variables.

In other words, they exist by default. Furthermore, developers should treat them like regular arrays.

When you access a GET variable in PHP, what you’re actually doing is accessing a GET variable that has been neatly packaged into an array called $_GET.

//$_GET is actually an array
echo $_GET['test'];

In the above piece of code, you are accessing an array element with the index “test”.

Avoiding index errors.

To avoid these errors, you can use two different methods.

The first method involves using the isset function, which checks to see if a variable exists.

//Check if the index "test" exists before accessing it.
if(isset($_GET['test'])){
    //It exists. We can now use it.
    echo $_GET['test'];
} else{
    //It does not exist.
}

The second method involves using the function array_key_exists, which specifically checks to see if an array index exists.

if(array_key_exists('test', $_GET)){
    //It exists
    echo $_GET['test'];
} else{
    //It does not exist
}

When you are dealing with GET variables and POST variables, you should never assume that they exist. This is because they are external variables.

In other words, they come from the client.

For example, a hacker can remove a GET variable or rename it. Similarly, an end user can inadvertently remove a GET variable by mistake while they are trying to copy and paste a URL.

Someone with a basic knowledge of HTML can delete form elements using the Inspect Element tool. As a result, you cannot assume that a POST variable will always exist either.