Question

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A comprehensive regex for phone number validation
PHP: Validation of US Phone numbers

I’m trying to validate a phone number using preg_match, but any time I type in the correct format of phone number [phone], it returns the invalid character error instead of true. I don’t think there’s anything wrong with my regex (as far as I know), so I’m guessing there’s something wrong with my logic

function validate_phone_number($phoneNumber, $requiredLength = 14)
{

       //Check to make sure the phone number format is valid 
    for ($i = 0; $i < strlen($_POST[$phoneNumber]); $i++){
            if(preg_match('/^\(\d{3}\) \d{3}-\d{4}\$/', $_POST[phoneNumber]{$i}))
            {
                return true;
            }
            else
            {
                return "<h3>" . "The phone number you entered contains invalid characters" . "</h3>";
            }

       //Check to make sure the number is the required length
            if (strlen($_POST[$phoneNumber]) > $requiredLength) {
                return "<h3>" . "The phone number you entered contains too many characters" . "</h3>";
            }
            else if (strlen($_POST[$phoneNumber]) < $requiredLength) {
                return "<h3>" . "The phone number you entered does not contain enough characters" . "</h3>";
            }
        }
        return true;
}

What I’m using to call the function

if (count($_POST) > 0) {
    $error = array();


   $phone = validate_phone_number('phoneNumber');
        if($phone !==true) {
            $error[] = $phone;

        }


        if (count($error) == 0) {

           //Phone number validates

        }

        else { 
          echo "<h2>Error Message:</h2>";

          foreach($error as $msg) {
            echo "<p>" . $msg . "</p>";
          }
        }
      }

Answer 1

Two things wrong here:

for ($i = 0; $i < strlen($_POST[$phoneNumber]); $i++){
        if(preg_match('/^\(\d{3}\) \d{3}-\d{4}\$/', $_POST[phoneNumber]{$i}))

Firstly you used phoneNumber as bare constant. But in the rest of your code you used $phoneNumber as name reference. Change that. (Better yet, pass the $value to your function, not a reference key to $_POST).

Secondly, you seem to be iterating over it character-wise {$i}. But the regex is supposed to be applied to the whole string. Curb the for.

function validate_phone_number($phoneNumber, $requiredLength = 14)
{    
    //Check to make sure the phone number format is valid 
    if (preg_match('/^\(\d{3}\) \d{3}-\d{4}\$/', $_POST[$phoneNumber]))
    {

The length check is entirely redundant, as the regex will already assert your fixed format.