How to solve an undefined array key error in PHP?

If you are getting an “undefined array key” error in your PHP code, then it normally means you are trying to access an array key that doesn’t exist. To avoid this error you can use the following approaches :

1. Check the array key before accessing it

Use isset() or array_key_exists() function available in PHP to check the array key before accessing it.

$myArray = array("key1" => "value1", "key2" => "value2");

// Using isset
if (isset($myArray["key3"])) {
    $value = $myArray["key3"];
} else {
    $value = "default value"; // or handle the situation accordingly
}

// Using array_key_exists
if (array_key_exists("key3", $myArray)) {
    $value = $myArray["key3"];
} else {
    $value = "default value"; // or handle the situation accordingly
}

2. Use the null coalescing operator

Using the null coalescing operator (??) is one of the efficient ways to assign a default value when a key is not present.

$myArray = array("key1" => "value1", "key2" => "value2");

$value = $myArray["key3"] ?? "default value";

3. Use the ternary operator

Similar to the coalescing operator you can also use the ternary operator to assign a default value when the key is not present.

$myArray = array("key1" => "value1", "key2" => "value2");

$value = isset($myArray["key3"]) ? $myArray["key3"] : "default value";