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One of the "requirement" strings in our validation script (validate.inc) is "ccnumber" (which
we've added to the original PHP validation code we created in Usable Forms for the Web). This means that we need to
look for this string as a substring of each field name in the form we're validating,
and if we've found it, a variable named $ccnumber
has been set to TRUE.
If it is, then we know we need to try to validate the current field as credit
card information.
if($ccnumber)
{First, we get rid of any spaces or dashes the user might have typed in, then
test the result to see if it's a numeric value ($not_int
is the regular expression /\D/, which matches any non-digit characters in a string):
$value = preg_replace("[ -]+","",$value);
if( $value!="" && preg_match($not_int, $value ) )
{If we find any non-digits in the value, we add an appropriate error message
onto the value of the variable $err_msg,
and set our validation flag $validated
to FALSE:
$err_msg .= "The <b>$field_name</b> should contain only
the digits 0-9.<br />\n";
$validated = FALSE;
}
else
{Otherwise, we check to see if the user has selected a credit card type:
if( isset($HTTP_POST_VARS["Credit0Card0Type_required"]) )
{If so, we get that type as the variable $cc_type,
the value in the Card Number field as $cc_number, and the length of that value as
$cc_length:
$cc_type = $HTTP_POST_VARS["Credit0Card0Type_required"];
$cc_number =
$HTTP_POST_VARS["Credit0Card0Number_ccnumber_required"];
$cc_length = strlen($cc_number);Now we test the length of the number against what's correct for its type,
setting $validated to TRUE or FALSE accordingly:
switch($cc_type)
{
case "MasterCard":
$validated = $cc_length == 16;
break;
case "Visa":
$validated = ($cc_length == 13 || $cc_length == 16);
break;
case "American Express":
$validated = $cc_length == 15;
break;
}If $validated is FALSE, the number has the wrong number of digits for
the type of card indicated:
if(!$validated)
$err_msg .= "Wrong number of digits for $cc_type.<br >\n";
else
{Otherwise, we check to see if the number has the correct prefix for that type:
switch($cc_type)
{
case "MasterCard":
$prefix = substr($cc_number, 0, 2);
$validated = $validated && ($prefix > 50 && $prefix < 56);
break;
case "Visa":
$prefix = substr($cc_number, 0, 1);
$validated = $validated && ($prefix == 4);
break;
case "American Express":
$prefix = substr($cc_number, 0, 2);
$validated = $validated && ($prefix == 34 || $prefix == 37);
break;
}
if(!$validated)
$err_msg .= "Invalid prefix for $cc_type number.<br />\n";
else
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Created: January 2, 2003
Revised: January 2, 2003
URL: http://webreference.com/programming/carts/chap7/3/3.html
