PHP: Refresh page on invalid form submit - php

Question

How can I refresh a page with a form on submission pending the outcome of the submitted data and display a result.
e.g I have a page with a form:
<form action="" method="post">
<input type="name" value="" name="name" placeholder="Your Name" />
<input type="button" name="submit" value="submit form "/>
</form>
The engine that handles the form is external, but required in the page:
require_once 'form_engine.php';
form_engine.php checks the input,
$success = "true";
$errorMessage = " ";
$name = $_POST['name'];
if ( $name == '') {
$errorMessage = 'Please enter your name';
$success = false;
}
else (if $success = true) {
// do something with the data
}
The form page contains the result:
<form action="" method="post">
<input type="name" value="" name="name" placeholder="Your Name" />
<input type="button" name="submit" value="submit form "/>
</form>
<p><?php echo $errorMessage; ?></p>
Will the error message get displayed after the form is submitted incorrectly? Or do I have to use a session to store it?

Answer 1

You need something like this:
if (!isset($_POST['name']))
instead of
if ( $name == 'name')
UPDATE
Try this, it should give you the idea:
<?php
$errorMessage = false;
if (isset($_POST['submit'])) {
if (!isset($_POST['name']) || $_POST['name']=='') {
$errorMessage = 'Please enter your name';
}
else {
// do something with the data
echo "Success!!";
}
}
?>
<form method="post">
<input type="name" value="" name="name" placeholder="Your Name" />
<input type="submit" name="submit" />
</form>
<p><?php if ($errorMessage) echo $errorMessage; ?></p>
Note: leaving out the action attribute will just submit the form to the current page
Note 2: The PHP here could very well be stored in another page. Using require() is the same as putting the code directly into the page.

Answer 2

You can use redirect on php side:
header('Location: www.mysite.com/index.php');

Answer 3

You seem to be a little confused in terms of the exact process that occurs in terms of rendering a page, as do some of those commenting. You do not need to use sessions to solve this problem. There is no need to store anything server-side between page requests because the user's browser with retain everything that you need, at least for this situation. My guess is the others took you mentioning an "external engine" and thought that the form would be submitting away to a different site/page.
form loops
Below is a diagram showing a typical form request loop:
You do not have to do this, as coding is as much about personal preference to anything else, but typically people will design their form to submit back to the same URI that generated it — as you seem to be doing in your example, by leaving the action attribute blank. By doing this, as long as you embed everything you wish to pass back to the server side within the form — each time the user submits — that information will be resent and be available in PHP.
Obviously you need to be wary of what information might constitute as sensitive, as this data should only ever be written into markup if your requests are protected by HTTPS/SSL. You should also filter/escape any user input to prevent markup injection into your site. You can prevent many problems by using htmlentities, however this can cause issues depending on the values you are trying to capture from the user. Because you are using double quoted HTML attributes (the right way to do them ;) I have not set the ENT_QUOTES option.
back to the point
So in the above loop the user will be shown the form for the first time, and after any subsequent submit, which means that each time your PHP notices that there is an error you can just add your message into the page flow. The trick with this kind of system is what exactly do you do once the form is fully complete. To get out of the loop most people will use a header location call:
<?php
require_once 'form_engine.php';
$name = !empty($_POST['name']) ? trim($_POST['name']) : '';
$name = htmlentities($name);
if ( $success ) {
header('location: next-step.php');
exit;
}
?>
<form action="" method="post">
<input type="name" value="<?php echo $name; ?>" name="name" placeholder="Your Name" />
<input type="button" name="submit" value="submit form "/>
</form>
<?php
if ( $errorMessage ) {
echo "<p>$errorMessage</p>";
}
?>
form engine repairs
You should also rectify your form_engine.php as per my comments above and Shekhar Joshi's answer, although I would keep the header code outside of your engine logic, and leave that decision to the code that requires in the engine — as the above does.

Answer 4

may be, you are looking for this! the header() method.
$success = true;
$errorMessage = " ";
$name = $_POST['name'];
if(isset($_POST['name'])) {
if ( $_POST['name'] == '') {
$errorMessage = 'Please enter your name';
$success = false;
header('Location: www.something.com/some.php');
}
else if ($success == true) {
// do something with the data
}
}