how initiate a validation form using php

Question

I am trying to do the following validation on my registration page;

at the beginning of the page I have,

<?php
if(!isset($_POST['sumbit']) && (!validateName($_POST['phonenumber'])) {
here html show errors if the form was submitted with errors
<form method= "post" action="<?php echo htmlspecialchars($_SERVER['PHP_SELF']);?>">
<div>Phone Number</div>
<input type="text" name="phonenumber" size="20" placeholder="phone" value="<?php echo htmlspecialchars($_POST['phonenumber']); ?>" required>
<input type="submit" name="submit" value="Next">
</form>

but I am getting "Notice: Undefined index: phonenumber in ...." before submit page

I have the validationName function in a separated file that I call from here but I am getting error

any help??

Answer 1

Try setting new var like $phn_number = isset($_POST['phonenumber']);

 if(!isset($_POST['sumbit']) && (!validateName($phn_number)) {

Its just a NOTICE, you may work even if continues.

Answer 2

It should be

if(isset($_POST['submit']) && (!validateName($_POST['phonenumber'])) {

notice the lack of '!' and you hava a typo 'sumbit'. But to make it simpler it could be

if(isset($_POST['phonenumber']) && (!validateName($_POST['phonenumber'])) {

Answer 3

You have to validate that the variable is set:

if(isset($_POST['var']))

or (for checking if it is not empty):

if(!empty($_POST['var']))

But you can just ignore notices, this is not the best solution, but they are not shown on productive environments. Furthermore, you can leave out this:

action="<?php echo htmlspecialchars($_SERVER['PHP_SELF']);?>"

For your error (variable not set), try this for displaying all POSTed things:

var_dump($_POST);

EDIT: There is another logical mistake:

if(!isset($_POST['sumbit']) && (!validateName($_POST['phonenumber'])) {

Should be this, to display something in case of error:

if(isset($_POST['submit']) && !validateName($_POST['phonenumber'])) {