PHP Superglobals
Superglobals are special arrays that PHP fills with values from a request. They are ready before the first line of code runs.
An empty $_GET array
No request exists on this machine, so nothing filled the array. The empty shape is the evidence.
<?php
print_r($_GET);An empty $_POST array
No form was submitted to this program. Its array prints the same empty shape.
<?php
print_r($_POST);Checking a key with isset
isset asks whether a key exists in an array. The answer is false here because the name key is absent.
<?php
var_dump(isset($_GET["name"]));Example
<?php
if (isset($_GET["name"])) {
echo "Name found\n";
} else {
echo "No name given\n";
}Key points
- The query string is the part of a page address after the question mark.
- $_GET holds the values from the query string.
- $_POST holds the values from a submitted form.
- Reading a key that is not there gives a warning.
- Checking a key before reading it is the safe habit.
In this example, isset checks the name key in $_GET. The key is absent, so the else branch runs. The program prints No name given.
Note
Superglobals can be read in any part of a program.
Try it Yourself
Edit the code, then press Run.
Running is simulated · Programiz PHP Compiler
Exercise
What does var_dump(isset($_GET["city"])) print when the city key is absent?