PHP Notice Undefined Index

Notice Undefined Index in PHP is an error which occurs when we try to access the value or variable which does not even exist in reality. Undefined Index is the usual error that comes up when we try to access the variable which does not persist. For instance, an array we are trying to access the index does not really exist in that, so in this scenario, we will get an Undefined Index in PHP. Undefined here means we have not defined its value and trying to access it.

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Syntax of PHP Notice Undefined Index

There is no such syntax defined for an undefined index in php because it a kind of error we get when we try to access the value or variable in our code that does not really exist or no value assign to them, and we are trying to access its value somewhere in the code.

$myarray = array(value1, value2, value3, so on..)
$myarray[value_does_not_exists]

In the above lines of syntax, we are trying to access the array by passing a key which does not exist in the array. So this will throw us an Undefined index error in runtime.

Let’s see one example of how we can do this while programming:

Code:

$myarray = array(100, 200, 300, 400)
$myarray[1000]

In this way, we can replicate this error in PHP, but this can be prevented by using isst() method in PHP to make our code working in such a situation.

How does Notice Undefined Index work in PHP?

As of now, we know that an undefined index is a kind of exception, or we can say error in PHP. This will occur if we want to access a variable that does not really exist in our program. This needs to be handled; otherwise, it will cause a serious issue to our application and termination of the program. We have some methods defined in PHP to handle this kind of error in a program.

Here we will see one sample piece of code and its working, how this occurs in the program and how it should be handle.

Example:

Code:

<?php
// Your code here!
$myarray = array('200','300','400', '500', '600', '700', '1000');
echo $myarray[4];
echo $myarray['Hello '];
?>

In the above code lines, we create one array named ‘$myarray’, and we have initialized its value with some string integers inside it. In the second line, we are trying to access the variable of the array by using the value assigned to it and also, we are using the index. So index ‘4’ is present in the array, so this line would work fine as expected, but immediately after this line, we have another line in which we are trying to access the array element by its key. So, in this case, we will get Notice: Undefined Index in PHP with line number mentioned in it. We will now see how we can prevent this from happening in our code; for this, we have two methods available in PHP that can be used before accessing the element or value from the array.

Given below are the methods:

1. array_key_exists()

This method is used to check whether the key is present inside the array or not before access its value. This method can be used where we are trying to access the array element, and we are not sure about this. So before using the variable’s value, we can check by using this method whether the element or key exists.

This method takes two parameters as the input parameter. The first line is the key and the second one is an array itself.

Let’s see its syntax of the method

Signature:

array_key_exists(your_key, your_array)

Here we pass two parameters the key we pass it checks it into the whole array. Its return type is Boolean; it will return true if the key is present in the array, else it will return false if the keys does not exist.

2. isset()

This method also checks variable is set in the program or not before accessing its value. It also checks for a NULL variable. It performs two things it; first checks variable is defined, and the other is it should not be NULL.

Signature:

isset(variables);

Here we can pass our variable, which we want to check before accessing them in the program. The return type for this method is also Boolean; if it found the variable and it is not NULL, then it will return as true as the value. If the previous condition not specified, then it will return False.

Examples of PHP Notice Undefined Index

Given below are the examples of PHP Notice Undefined Index:

Example #1

In this example, we are trying to access the key that does not access the array, so while program execution, we will get Notice Undefined Index error in PHP.

Code:

<?php
// Your code here!
// creating an array here
$myarray = array(0=>'Hi',1=>'Hello',2=>'To', 3=>'All', 4=>'Stay', 5=>'Safe', 6=>'Enjoy !!');
//try to print values from array
echo $myarray[0]."\n";
echo $myarray[1]."\n";
echo $myarray[2]."\n";
//trying to access the element which does not exists.
echo $myarray['World']."\n";
?>

Output:

Example #2

To prevent this error while occurring in program execution.

Code:

<?php
// Your code here!
// creating an array here
$myarray = array(0=>'Hi',1=>'Hello',2=>'To', 3=>'All', 4=>'Stay', 5=>'Safe', 6=>'Enjoy !!');
//try to print values from array
echo $myarray[0]."\n";
echo $myarray[1]."\n";
echo $myarray[2]."\n";
//trying to access the element which does not exists.
if(array_key_exists('World', $myarray)){
echo "Key exists in array !!";
}else {
echo "Key does not exists in array !! :)";
}
?>

Output:

Conclusion

Notice Undefined Index is a kind of error we got in PHP when we try to access the non-existing element from the array or in our program. One more case is that it can occur when we try to access a NULL value in the program. So we can use two methods, isset() and array_key_exists() methods in PHP, to overcome this error in the application.

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