Key check with isset()
Learn to check a key with isset() and the difference from array_key_exists().
Checking keys with isset()
You check whether a key exists in an array with isset(). isset($user["phone"]) returns true if the key exists and its value is not null; otherwise it returns false. No warning is emitted.
For example if a phone number is optional you test with isset first and print it only when present. This avoids the warning from accessing a missing key directly.
null values and key checks
Sometimes a key exists in the array but its value is null. isset() returns false in this case; it treats null values as unset. array_key_exists() only checks that the key exists and returns true for a null value.
Example: with $user = ["phone" => null], isset($user["phone"]) returns false and array_key_exists("phone", $user) returns true. isset is enough for most cases; if the distinction "key set to null on purpose" matters, use array_key_exists.
Exercise Phone check
Create the $user associative array with "name" => "Alex" and "email" => "alex@mail.com". Check the "phone" key with isset(); if it exists print it, otherwise print No phone.
Show example solution
Use the structure if (isset($user["phone"])) { ... } else { echo "No phone\n"; }
Example solution:
<?php
// User and phone check
$user = ["name" => "Alex", "email" => "alex@mail.com"];
if (isset($user["phone"])) {
echo $user["phone"] . "\n";
} else {
echo "No phone\n";
}Test yourself
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What is the difference between isset() and array_key_exists()?
- isset() returns true for a null value, array_key_exists() returns false
- They are the same
- isset() checks only numeric keys
- isset() returns false for a null value, array_key_exists() returns true
Show answer
isset() returns false for a null value, array_key_exists() returns true — Correct. isset() returns false for null; array_key_exists() returns true when the key exists.
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Complete the isset call
if (____($user["phone"])) { echo $user["phone"]; }Show answer
if (isset($user["phone"])) { echo $user["phone"]; } -
Match each function to its behavior
- isset($a["x"])
- returns false if key missing
- array_key_exists("x", $a)
- returns true if key exists
- $a["x"] ?? "y"
- returns "y" if key missing