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.

You're asking it to "start search at offset 0", not "stop searching after offset 0". Try `in_array($array[$i][0], array('R', 'r'))` instead. — DCoder, Nov 13 '12 at 07:47
@DCoder Yes thank you, I saw this on internet ! But why === 0 isn't it supposed to be FALSE? Why should I put it outside the function? Can you please explain me this, I'll accept your answer. — Ydhem, Nov 13 '12 at 07:49

score 5 · Accepted Answer · answered Nov 13 '12 at 07:50

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') { ... }

@Yoshi: that's probably slower than just checking the first symbol directly. Not significantly, but still. — DCoder, Nov 13 '12 at 08:15

score 1 · Answer 2 · answered Nov 13 '12 at 07:52

1

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;)

answered Nov 13 '12 at 07:52

Louis Huppenbauer

3,719
1
18
24

Thank you for this alternative. – Ydhem Nov 13 '12 at 07:55

Understanding stripos offset?

2 Answers2