if offset in php code example

Example 1: keys of array exist in array

function findKey($array, $keySearch)
{
    foreach ($array as $key => $item) {
        if ($key == $keySearch) {
            echo 'yes, it exists';
            return true;
        } elseif (is_array($item) && findKey($item, $keySearch)) {
            return true;
        }
    }
    return false;
}

Example 2: php undefined offset

If preg_match did not find a match, $matches is an empty array. So you should check if preg_match found an match before accessing $matches[0], for example:

function get_match($regex,$content)
{
    if (preg_match($regex,$content,$matches)) {
        return $matches[0];
    } else {
        return null;
    }
}