Validating POST fields the easy way

Validating POST data from a form is a common requirement for a developer. If the number of form fields are few than the validation is a small matter. But the case is different when the form contains more than 15 or 20 fields and some of the fields are mandatory. The following code will give you an idea of how to easily validate mandatory fields, whatever the number of fields.

The first step is to prefix a ‘c_’ or any other character of your choice to a form field that is mandatory. For example I’ve prefixed a ‘c_’ for the email field below.

<input name="c_email" id="c_email" maxlength="40" type="text" />

Once we have added the required prefix we can check for them using the following code.

/* Initialize $_SESSION variables to hold errors and form variables */
$_SESSION['formVars'] = array();
$_SESSION['errors'] = array();
/* Copy all $_POST variables to $_SESSION['formVars'] */
foreach($_POST as $varname=>$value) 
     * For form elements that are compulsory check 
     * to see if they are empty. To ease this ,form 
     * elements that are compulsory have a 'c_' prefix added,
     * we can use that to parse the compulsory fields.
     /* Get the field prefix */
    $prefix = substr($varname, 0, 2);
    if(empty($_SESSION['formVars'][$varname]) && $prefix == "c_")
        $_SESSION['errors'][$varname] = substr($varname, 2, strlen($varname) - 2) . " field cannot be empty";

Now it doesn’t matter how many form fields you have, the code remains the same. You can extend the idea for other validation purpose. For example you can add a double prefix like ‘ci_” to indicate that the field is mandatory with a integer datatype and make the corresponding change in the validation code.

This site is a digital habitat of Sameer Borate, a freelance web developer working in PHP, MySQL and WordPress. I also provide web scraping services, website design and development and integration of various Open Source API's. Contact me at metapix[at] for any new project requirements and price quotes.

6 Responses


Justin Woods

December 15th, 2008 at 5:08 pm

Hey there. Why not use PHP’s built-in ability to automaticaly create arrays from submitted data?



$form_data = $_POST[‘c’];

Using an array, there’s no need to loop through your submitted data to find fields with a prefix.


Justin Woods

December 15th, 2008 at 5:09 pm

Hmmm… My HTML got removed…

Here’s another try:

> type=”text” name=”c[first_name]” / <
> type=”text” name=”c[last_name]” / <



December 16th, 2008 at 2:34 am

I think in this area, there oh… about 7368 different ways.

Typically, I go for this model:

$v )
if( ! ereg( $v , $_POST[$k] ) )
$errors[$k] = “INVALID…”;




December 16th, 2008 at 2:35 am

Sorry you comment system hates me… :(

$regs[‘user_name’] = “^[a-zA-Z][a-zA-Z]*$”;
$regs[‘user_fname’] = “^[a-zA-Z][a-zA-Z]*$”;

foreach( $regs as $k => $v )
if( ! ereg( $v , $_POST[$k] ) )
$errors[$k] = “INVALID…”;


Mère Teresa

December 16th, 2008 at 5:46 am



March 17th, 2009 at 1:03 am

Hey… Do you really think it could be safety?
What if I edit HTML source and send it to server? just using mozilla firebug extension – its the easiest way.

I think all data must be validate on a server side.

Your thoughts

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