In this section, we introduce validation on the server using PHP.We show you how to validate numbers including currencies and credit cards, strings including email addresses and Zip Codes, and dates and times.Strings are popular for two reasons: first, all data from a form that is stored in the superglobals is of the type string; and, second, some nonstring data such as a date of birth or a phone number is likely to be stored as a string in a database table because it may contain brackets, dashes, and slashes.However, despite dates and phone numbers being sometimes stored as strings, we discuss their validation in Section 9.2.2.5.

If the domain isn't an `MX', the domain is checked with gethostbyname( ) to see if it has an `A' record; the relevant standard RFC-974 states that when a domain does not have an `MX', it should be interpreted as having one equal to the host name.

For example, an address such as the following is valid: If any email test fails, an error message is output, and no further checks of the email value are made. The first check tests to make sure that an email address has been entered. It then uses a regular expression to check if the email address matches a template.

It isn't RFC-2822-compliant but works reasonably for most email addresses: The function is imperfect.

We show how to extend and integrate this approach further in Chapter 10 so that the batch errors are reported as part of a customer form, and we show a completed customer entry form and validation in Chapter 17.

Testing whether mandatory fields have been entered is straightforward, and we have implemented this in our examples in Chapter 8.