Consider this code segment:
if (empty($_GET)) {
$page_number = 1;
} else {
$page_number = $_GET["page_number"];
}
I wonder if there is a better, more succinct way to express that idea. I thought about using a ternary operator, but the improvement over the original is not substantial:
$page_number = empty($_GET) ? 1 : $_GET["page_number"];
EBrown has a good answer already, where he shows which steps has to be taken to make sure the page number is set correctly. He also comes up with a handy function. Let me show you another approach, using build-in functionality in PHP to handle the given problem.
Filter the input
Make use of PHPs filter_input:
$page_number = filter_input(INPUT_GET, 'page_number', FILTER_VALIDATE_INT);
It uses a predefined validation filter called FILTER_VALIDATE_INT, that …
… validates value as integer, optionally from the specified range, and converts to int on success.
So $page_number will be of type int and not string in case of success. If the filter fails, $page_name will be null|false:
Value of the requested variable on success, FALSE if the filter fails, or NULL if the variable_name variable is not set. If the flag FILTER_NULL_ON_FAILURE is used, it returns FALSE if the variable is not set and NULL if the filter fails.
Should I always default to 1?
Like in your question, if $page_number is not set at all, you should set it to 1. Using filter_input as described before you can test this case like:
if (null === $page_number) {
$page_number = 1;
}
But there are more cases to be handled like:
-1|0|10000001hello-world|a4fe|1.2I recommend to not to default to 1 in any of these cases, but to show a 404 error page instead.
To make sure the integer value of $page_number will produce a valid page, you can take it one step further and set a range for the filter. The complete example would look like
$page_number = filter_input(
INPUT_GET,
'page_number',
FILTER_VALIDATE_INT,
['options' => ['min_range' => 1, 'max_range' => 104]]
);
if (false === $page_number) {
// show 404 page
}
if (null === $page_number) {
$page_number = 1;
}
1 Unless you have 1000000 or more pages of course.
You have a surprise bug: what happens when I do page.php?Name=EBrown? Well $_GET is not empty but your page_number sure isn't set.
That said, you should be doing something like the following:
$page_number = 1;
if (isset($_GET["page_number"})) {
$page_number = $_GET["page_number"];
}
or
$page_number = $_GET["page_number"];
if (!isset($page_number)) {
$page_number = 1;
}
The first defaults and then checks for the parameter, the second checks if it's set then defaults. Take your pick.
But those still don't handle invalid (non-numeric) input, so we can do that as well:
$page_number = $_GET["page_number"];
if (isset($page_number) === FALSE || is_numeric($page_number) === FALSE) {
$page_number = 1;
}
Now we safely default to 1 when page_number is not set, or when it's not numeric.
Of course, we still have another bug: what happens if page_number is 1.12? That's probably unintended. So, we'll check for that as well:
$page_number = $_GET["page_number"];
if (isset($page_number) === FALSE || strpos($page_number, '.') !== FALSE || is_numeric($page_number) === FALSE) {
$page_number = 1;
}
And finally we'd extract that to a method:
function defaultInt($intValue, $default) {
if (isset($intValue) === FALSE
|| strpos($intValue, '.') !== FALSE
|| is_numeric($intValue) === FALSE) {
return $default;
}
return $intValue;
}
$page_number = defaultInt($_GET["page_number"], 1);
Easy to use in the future as well.
page?page_number=%2B5 and page?page_number=-5 will pass your function ., page?page_number=0x5 will pass too if you are before php 7.0.0 . although a string variable equals "+5" or "-5" will be evaluated as integer in a mathematical context in loosely typed language like php . but this is might not be your intended behavior of the function.
\$\endgroup\$
if you want to try the shorthand of that equation, you can go for
$pageNumber = isset($_GET['page_number']) && intval($_GET['page_number']) > 0 ? $_GET['page_number'] : 1
This will check, if the page_number is set or not. If set then is the value greater than 0 then get the page number, otherwise set to 1.
