What does ? … : … do? [duplicate]

Question

This question already has an answer here:

• What are the PHP operators “?” and “:” called and what do they do? 9 answers

$items = (isset($_POST['items'])) ? $_POST['items'] : array();

I don't understand the last snippet of this code "? $_POST['items'] : array();"

What does that combination of code do exactly?

I use it to take in a bunch of values from html text boxes and store it into a session array. But the problem is, if I attempt to resubmit the data in text boxes the new array session overwrites the old session array completely blank spaces and all.

I only want to overwrite places in the array that already have values. If the user decides to fill out only a few text boxes I don't want the previous session array data to be overwritten by blank spaces (from the blank text boxes).

I'm thinking the above code is the problem, but I'm not sure how it works. Enlighten me please.

Answer 1

It is the same as:

if (isset($_POST['items']){
    $items = $_POST['items'];
} else {
    $items = array();
}

Answer 2

Basically if $_POST['items'] exists then $items gets set to it otherwise it gets set to an empty array.