Validating $_POST data

The primary difference between filtering and validation is that the latter does not alter the original data. Another difference is in intent. The purpose of validation is to confirm that the data matches certain criteria established according to the needs of your customer.

How to do it...

1. The basic validation mechanism we will present here is identical to that shown in the preceding recipe. As with filtering, it is vital to have an idea of the nature of the data to be validated, how it fits your customer's requirements, and also whether it matches the criteria enforced by the database. For example, if in the database, the maximum width of the column is 128, the validation callback could use strlen() to confirm that the length of the data submitted is less than or equal to 128 characters. Likewise, you could use ctype_alnum() to confirm that the data only contains letters and numbers, as appropriate.
2. Another consideration for validation is to present an appropriate...