"Cannot modify header information - headers already sent by..." error

[doel.jangkrik]

I am trying to make a login page using php.

index.php contain form for "login" and "password" which will be check by "process.php"

My intention is: if the login or password is incorrect, an alert box will pop up telling the user the case, and redirect back to index.php

Here is the code for process.php

<?php
session_start();
include('db.php');

if(isset($_POST['submit'])) :
	// Username and password sent from signup form
	// Remove all HTML-tags and PHP-tags
	$username = strip_tags($_POST['username']);
	$password = strip_tags($_POST['password']);

	// Make the query a wee-bit safer
	$query = sprintf("SELECT ID FROM users WHERE username = '%s' AND user_password = '%s' LIMIT 1;", mysql_real_escape_string($username), mysql_real_escape_string($password));
	
	$result = mysql_query($query);
	if(1 != mysql_num_rows($result)) :
	// MySQL returned zero rows (or there's something wrong with the query)

		echo "<script>alert('Wrong login or password')</script>"; 
		header('Location: index.php');
	else :
		// We found the row that we were looking for
		$row = mysql_fetch_assoc($result);
		
		// Register the user ID for further use
		$_SESSION['member_ID'] = $row['ID'];
		header('Location: members-only.php');
	endif;
endif;
?>

I got the error message in "cannot modify header information". From the php textbox that I got, I know that the error was caused because I put "echo" code before "header"

Is there anyway to achieve what I want to do without putting anything before the header?

Thanks!

[somedude3488]

you can't use header() like that. you would need to make the javascript redirect using:

window.location = 'index.php';

[yara1]

hi

mmmmm

i meet this error many time

only start ur code from first line

dont leave lines b4 <?php

[phpuser]

hi,

As in above reply you cant have to left any line before code starting

and one thing is that , you include file like include('db.php');

so you have to check if there is another session_start(); in your db.php file then also you get this same error.

check all thing and run it again you sure get output :)

[doel.jangkrik]

thanks everyone for your help!

I just use kkeith29 suggestion to redirect using javascript.