How many variable checks should you do? [closed] - php

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Something I've never been sure about is how many variable checks to do in PHP. For example take the following piece of code. I am not checking any of the variables before I assign them or pass them to a function to see if they contain what I expect
$carId = '12';
$aCar = fetchCar($carId);
$make = $aCar['make'];
$model = $aCar['model'];
$yearMade = $aCar['year'];
$age = calcAge($yearMade);
Now if I add some checks
$carId = '12';
if(is_numeric($carId))
{
$aCar = fetchCar($carId);
if(isset($aCar['make']) && is_string($aCar['make']))
{
$make = $aCar['make'];
}
else
{
//Report error
}
if(isset($aCar['model']) && is_string($aCar['model']))
{
$model = $aCar['model'];
}
else
{
//Report error
}
if(isset($aCar['year']) && is_numeric($aCar['year']))
{
$yearMade = $aCar['year'];
$age = calcAge($yearMade);
}
else
{
//Report error
}
}
else
{
//Report errors
}
The code is now better but is it a bit too excessive and bloated? Should I be doing this many checks?
If I shouldn't be doing this many checks where do you draw the line between what you should and shouldn't check?

Answer 1

This is the dilemma of a dynamic type language.
It depends heavily on what fetchCar() function is doing.
The approach i would take is assume fetchCar is returning a car array or throwing exception.
If you combine this with good exception handling logic you can end up with clean and stable code.
For example:
function fetchCar($id) {
$car = queryDatabaseSomehow();
if (empty($car)) {
throw new ExceptionNotFound();
}
//eventually you can put your type checking here?
if (!isset($car['x']) || !is_string($car['x'])) {
throw new ExceptionDb();
}
}
echo fetchCar(3)['make'];
Also if you would like to do this super-proper and go fully OOP, Car should become a class with make,model and year as its members. fetchCar() would return Car or throw Exception. But this is not always desirable of course.

Answer 2

One issue that some people haven't noticed. Be wary of using is_string:
<?php
$var = "test";
$var['something'] = 2;
if(is_string($var['something'])) {
echo "Hello world!"; // Will echo this because $var is a string!
} else {
echo "Hello hell!";
}
echo "<br/>";
echo $var['something']; // returns 2
?>
PHPFiddle.
Compare it with this:
$var = array('something' => 2);
if(is_string($var['something'])) {
echo "Hello world!"; // $var is now an array
} else if (is_numeric($var['something'])) {
echo "Hello hell!"; // Will echo this because $var is string!
}
echo "<br/>";
echo $var['something'];
You need to check whether $var is an array, as it might give you unexpected results. isset($var['something']) will return true in the first example.
To answer your question, I don't think those are too many checks. It really depends on what fetchCar() does and how it gets the data. If you can't trust it (say, it's based on user data) then you should perform all these checks. If not, then there is no point really.

Answer 3

I rather turn it all into a function that can be reused for these cases.
function check_keys($arr_check, $arr_cond) {
$boo_success = TRUE;
foreach(array_keys($arr_cond) as $h)
if (in_array($arr_cond[$h], array('is_string', 'is_numeric'))) {
if ( ! isset($arr_check[$h]) or ! ($arr_cond[$h]($arr_check[$h]))) {
$boo_success = FALSE;
echo "The key {$h} is missing!";
// If run through a class, $this->errors[] = 'error message';
}
} else {
$boo_success = FALSE;
echo 'Invalid function';
}
return $boo_success;
}
$arr_keys = array('make' => 'is_string',
'model' => 'is_string',
'year' => 'is_numeric');
if (check_keys($aCar, $arr_keys)) {
// Run successful stuff
}