Understanding stripos offset?

Question

Let's say I've a small array () :

    $array = array(
        'Pantin',
        'Paris',
        'Paris',
        'Puhahaa',
        'Ptdr',
        'Roumanie',
        'Rlolo'
    );

What I want to do? Simply get all words that start with the 'r' letter

$dataLen = sizeof($array);
$results = array();

for ($i = 0; $i < $dataLen && count($array) < 10; $i++) {
    if (stripos($array[$i], 'r', 0)) { // 

        array_push($results, $array[$i]); 
    }
}

print_r($results); // Output : Array ( [0] => Paris [1] => Paris [2] => Ptdr )

I can't understand.. I put 0 as the offset, but it gives me words that start with the P letter and that "contain" the R letter.

Answer 1

Zero is the default value, so these things are equivalent;

stripos($array[$i], 'r', 0)
stripos($array[$i], 'r') // Same

That is, they start at position 0 and try to find the letter r or R. If it is not on position 0, they check the second letter, then the third letter etc.

Stripos returns the position of the found letter. For Paris is returns 2, for Rlolo it returns 0. If it is not found it returns false.

By default, 0 and false are both interpreted as false. So if the first letter is R, stripos returns 0 and the if statement is not executed. To solve this, use this code:

if (stripos($array[$i], 'r') !== false) { ... }

If you want to check just the first letter and not the subsequent letters, you can do something like this:

$word = $array[$i];
$firstLetter = $word[0];
if ($firstLetter == 'r' || $firstLetter == 'R') { ... }

Answer 2

Another method would be using array_filter with a callback.

$results = array_filter($array, function($var) {
    return strtolower($var[0]) == 'r';
});

(Of course you could also use return stripos($var, 'r') === 0;)