PHP replacing special characters like à->a, è->e

Question

I have php document signup.php which save the content from form (in form.php document) to MySQL base. The problem arises when I want to reformat the input content. I want do

Answer 1

Simple function. Transform strings like 'Ábç Éfg' to 'abc_efg'

/**
 * @param $str
 * @return mixed
 */
function sanitizeString($str) {
    $str = preg_replace('/[áàãâä]/ui', 'a', $str);
    $str = preg_replace('/[éèêë]/ui', 'e', $str);
    $str = preg_replace('/[íìîï]/ui', 'i', $str);
    $str = preg_replace('/[óòõôö]/ui', 'o', $str);
    $str = preg_replace('/[úùûü]/ui', 'u', $str);
    $str = preg_replace('/[ç]/ui', 'c', $str);
    $str = preg_replace('/[^a-z0-9]/i', '_', $str);
    $str = preg_replace('/_+/', '_', $str);

    return $str;
}