Check if a string starts with a substring from an array of substrings and return that substring

Question

I have an array with all German telephone area codes that is 5266 items long and looks like this:

$area_codes = array(
    '015019',
    '015020',
    '01511',
    '01512',
    '01514',
    '01515',
    '01516',
    '01517',
    '015180',
    '015181',
    '015182',
    '015183',
    '015184',
    '015185',
    'and so on'
);

I also have strings of telephone numbers that look like this:

015169999999

That is, the telephone number strings consist only of digits, without spaces, dashes, parentheses or other characters that are often used to visually structure telephone numbers.

I want to split the area code from the subscriber number and assign each to a separate variable. For the example number above, the expected result would be:

echo $area_code;
01516
echo $subscriber_number;
9999999

To identify the area code within the string, I am looping through the array of area codes:

foreach ($area_codes as $area_code) {
    if (str_starts_with($telephone_number, $area_code) == TRUE) {
        echo $area_code;
        $subscriber_number = str_replace($area_code, "", $telephone_number);
        echo $subscriber_number;
        break;
    }
}

How can I return the area code without looping?

---

Solutions like this require that I know where to split the string, but the area codes have different lengths.

Answer 1

You can still use the foreach, and then return an array with 2 values if there is a match, so you return early from the loop.

Note that you don't need the equals check here because str_starts_with returns a boolean.

if (str_starts_with($telephone_number, $code)) {

Example

$telephone_number = "015169999999";

foreach ($area_codes as $code) {
    if (str_starts_with($telephone_number, $code)) {
        $result = [$code, substr($telephone_number, strlen($code))];
        break;
    }
}

var_export($result ?? null);

Output

array (
  0 => '01516',
  1 => '9999999',
)

See a PHP demo.

I don't know if you can have multiple areacode matches for a single phone number, but if you want the longest to match first, you might sort your array beforehand starting with the longest string.