noob: how to show login error message on the same page after php server processes request

I have a login page. User first enters information and submits the form.

And I have a php script that will see if the user exists.

If( authenticated == true)  
{  
    // I do a redirect  
}  
else  
{  
  // I want to popup an error message on the same p开发者_如何学Cage.  
} 

1) I'm not sure how to show the popup message, I would like to make my div element visible with an error message returned from the server,

I would have to use Ajax, right? But how?

Or are there alternatives which are just as good.

---

if you would use ajax, use it for the whole process. So, no such problems at all. Get response and show it to user.

But as you stated yourself as a newbie, I'd strongly advise you to do it straight and simple way, just to learn how the things are.

As a general rule, a redirect always preferred after POST method request. In some cases one can omit this, but for the login form you would use a session anyway. So, you can start a session, write an error information there and then do Location: redirect.

After it, check session for the errors, and then notify user using any method you wish: a div, or a popup or anything.

---

If the form is posted to the same page, why not just use variables to display the error messages?

<?php

if (strlen($_POST['text']) < 5)
{
 $error['text'] = "Too short";
}

?>

<?php

if (isset($error['text']))
{
// Print errors at each form element?
}

?>

Hide & show DIVs using Javascript: http://csscreator.com/node/708

---

I would put the login page in a separate .HTML that you can run

$login = file_get_contents('login.html);

and in that markup put <!-- ERROR --> which you can then run a

$login = str_replace('<!-- ERROR -->', $error, $login); 

to insert any text you want and when you're all done

print $login;

---

The simplest answer is to just place a php if condition where you want the message to appear. No need for ajax.

some text above

<?php if (! $authenticated) { echo '<div class="error">'.$your_error_message.'</div>'; } ?>

some text below

I don't know what $authenticated in your case means, but make sure it includes a check that there were post variables also, otherwise the error message will show up on the login page in the pre-submitted use case.

---

Possibly simplest way to

function render_auth($errors = false){
?>
   <form action="/someURL">
     <? if($errors) echo $errors ?>
     <label>User name<input name="user_name"/></label><br/>
     <label>Password<input name="user_password" /></label><br/>
     <input type="submit"/>
   </form>
<?
};

On first call to the authentication page/controller you'd call render_auth() then on processing the auth call, if there was an error you'd call it render_auth("Missing password.") or such.

Generally stuff like this is pretty trivial if you're using a Templating system for you're views but if not, this function emulates templating to an extent.