Display error if empty field - PHP - php

Question

I want to display an error on the same page if any field is empty.
I've got this, which works but the empty error is displayed as soon as the page is loaded instead of appearing once empty fields are submitted.
<?php
// Required field names
$required = array('triangleSide1', 'triangleSide2', 'triangleSide3');
// Loop over field names, make sure each one exists and is not empty
$error = false;
foreach($required as $field)
{
if (empty($_POST[$field]))
{
$error = true;
}
}
if ($error)
{
echo "ALL FIELDS ARE REQUIRED";
}
else
{
echo header('Location: formSuccess.php');
}
?>
Any ideas? -- UPDATE // IVE TRIED ALL ANSWERS, nothing has worked so far

Answer 1

Wrap everything you check on post in this:
if (strtolower($_SERVER['REQUEST_METHOD']) == 'post')
{
// Your code containing checks here
}
This way, it will only trigger when a POST request is used.

Answer 2

If you have an input you know will always be submitted with the form, such as a hidden one:
<input type='hidden' name='formsubmit' value='1'>
Then you can test for this before validating the other inputs
if($_POST["formsubmit"]) {
// Required field names
$required = array('triangleSide1', 'triangleSide2', 'triangleSide3');
// Loop over field names, make sure each one exists and is not empty
$error = false;
foreach($required as $field) {
if (empty($_POST[$field])) {
$error = true;
}
}
if ($error) {
echo "ALL FIELDS ARE REQUIRED";
} else {
header('Location: formSuccess.php');
}
}
Also you don't echo the return of header()

Answer 3

OR another way ( I have something similar in one of my pages)
function check_presence($value){
return isset($value) && $value!=="";
}
function validate($required){
global $error
foreach($required as $field){
$value = trim($_POST[$field]);
if (!check_presence($value)){
$error = true;
}
}
return $error;
}
then on the page containing the form and its validation code
$required = array('triangleSide1', 'triangleSide2', 'triangleSide3');
if(isset($_POST["submit"]){
$error = validate($required);
if ($error){
echo "ALL FIELDS ARE REQUIRED";
}
}

Answer 4

Try isset instest of empty!!!
if (empty($_POST[$field]))
Become
if (isset($_POST[$field]))