Preserve form values on validation - php

Question

Ik want to prevent field reset after validation. I have searched some topics but i cant implement it in my code.
if($form_view == true) {
echo '';
if($error != '') {
echo '<strong><font color="#FF0000">Fout:</font></strong><br />'.$error.'<br />';
}
echo '<form method="POST" action="'.$filename.'" style="border:0px; margin:0px; padding:0px;">
Voornaam
<br />
<input type="text" name="voornaam" maxlength="50" id="input_contact" style="width: 200px; value="'.(isset($_POST['voornaam']) ? $_POST['voornaam'] : '').'">
<br />
Achteraam
<br />
<input type="text" name="achternaam" maxlength="50" id="input_contact" style="width: 200px; value="'.(isset($_POST['achternaam']) ? $_POST['achternaam'] : '').'">
<br />
Adres
<br />
<input type="text" name="adres" maxlength="50" id="input_contact" style="width: 400px; value="'.(isset($_POST['adres']) ? $_POST['adres'] : '').'">
<br />
Postcode <h7><i><small>(1234 AB)</small></i></h7>
<br />
<input type="text" name="postcode" maxlength="7" id="input_contact" style="width: 100px; value="'.(isset($_POST['postcode']) ? $_POST['postcode'] : '').'">
<br />
Woonplaats
<br />
<input type="text" name="woonplaats" maxlength="50" id="input_contact" style="width: 200px; value="'.(isset($_POST['woonplaats']) ? $_POST['woonplaats'] : '').'">
<br />
Telefoonnummer <h7><i><small>(0123-456789)</small></i></h7>
<br />
<input type="text" name="telefoonnummer" maxlength="11" id="input_contact" style="width: 100px; value="'.(isset($_POST['telefoonnummer']) ? $_POST['telefoonnummer'] : '').'">
<br /><br />
If you can give me one example on how to implement this in one field.
Thanks a lot

Answer 1

If the post is not made to this specific page they're landing on then the $_POST variable will not contain that information.
The quick and dirty of it is to save the information submitted in the $_SESSION[] as an array.
When the form is submitted, in addition to doing whatever you're currently doing, you need to save the information submitted into the session on the receiving script.
if ($_POST['submit']) {
// repeat or configure as desired to save submitted fields into Session
$_SESSION['form_info']['email_address'] = $_POST['email_address'];
}
On the form page itself you would use the following
if (isset($_SESSION['form_info'])) {
// You'll want to most likely consider filtering these using appropriate functions.
<input type="text" name="email_address" maxlength="50" id="email_address" style="width: 200px; value="<?php if (isset($_SESSION['form_info']['email_address']) { $_SESSION['form_info']['email_address']; } ?>">
}

Answer 2

Is the form action variable $filename referring to this particular php file or somewhere else where validation happens? If the form action happens somewhere else, the Moylin's answer is your solution (using $_SESSION). Otherwise, if possible, it's reasonable and simple to do the validation right here. echoing $_POST to value fields, as you did, should be sufficient enough (you dont even need the ternary operation there, if you want short code).
<form method="POST" action="thisPhpFile.php" >
value ="'. #$_POST['voornaam'] .'"
In the validation part (before echoing the form), you naturally want to check for all the errors, required fields etc. If everything is valid just point user to wanted location. Something along these lines:
if(isset($_POST['mySubmit'] {
//check errors/validate
if($valid == true) {
Header("Location: yourLocation.php");
}
}
else {
//echo your form here
}