How can I display the error message after submitting the form in php?

Question

I have a webpage which displays content after a selection and it contains a form with a submit button. Once the submit button is clicked I want to display the error messages in the previous page. Here is the code:

    //form is sending email through action:"email.php". Code in php file:   
    mail ($to, $subject, $mess);

    //set the error session...(I left out the form validation code to simplify)
    $_SESSION["Login.Error"] = "Invalid credentials";

    //go back to previous page with all previous selections
    $previousPage = $_SERVER['HTTP_REFERER'];
    header("Location: $previousPage");

In the form I added the following code to display the error message:

<p class="form-text text-muted">Error Message: 
   <?php if(isset($_SESSION['Login.Error']))  {
   echo $_SESSION['Login.Error'];
   unset($_SESSION['Login.Error']); }
   ?> 
</p>

After pressing submit the previous page is loading OK, but the error message is not displaying, so there is something wrong with the $_SESSION I guess. Or does this have to do with $_SERVER['HTTP_REFERER'];? Can somebody help?

Answer 1

You can use session_start();

   session_start();

   mail ($to, $subject, $mess);

  //set the error session...(I left out the form validation code to simplify)
  $_SESSION["Login.Error"] = "Invalid credentials";

  //go back to previous page with all previous selections
  $previousPage = $_SERVER['HTTP_REFERER'];
  header("Location: $previousPage")

/* referer page */

   <?php session_start();?>

  <p class="form-text text-muted">Error Message: 
         <?php if(isset($_SESSION['Login.Error']))  {
          echo $_SESSION['Login.Error'];
          unset($_SESSION['Login.Error']); }
  ?> 
  </p>

Answer 2

You need to start session as per below code.

<?php 
    session_start();
    mail ($to, $subject, $mess);

    $_SESSION["Login.Error"] = "Invalid credentials";
    $previousPage = $_SERVER['HTTP_REFERER'];
    header("Location: $previousPage");
?>

In the form I added the following code to display the error message:

<p class="form-text text-muted">Error Message: 
   <?php 
   session_start();
   if(isset($_SESSION['Login.Error']))  {
       echo $_SESSION['Login.Error'];
       unset($_SESSION['Login.Error']);
   }
   ?> 
</p>