header is executed directly - php

Question

I am using a if condition and in that there is some script and then header.
But the script wont work and directly header works.
if(strpos(mysql_error(),'Email')!=false)
{
print '<script type="text/javascript">';
print 'alert("The email address is already registered")';
print '</script>';
header('Location: register.php');
}

Answer 1

Replace header with typical JS. That does the trick.
if(strpos(mysql_error(),'Email')!==false)
{
echo ("<SCRIPT LANGUAGE='JavaScript'>
window.alert('The email address is already registered')
window.location.href='register.php';
</SCRIPT>");
}

Answer 2

There are a few different things wrong in your code.
First, the header calls should be the first thing you output. You don't do that. You have unbuffered prints before it. From the (very good) PHP documentation:
Remember that header() must be called before any actual output is sent, either by normal HTML tags, blank lines in a file, or from PHP. It is a very common error to read code with include, or require, functions, or another file access function, and have spaces or empty lines that are output before header() is called. The same problem exists when using a single PHP/HTML file.
Second, even if you would have used buffered output, the Javascript would never execute as the body is not evaluated when there is a Location header.
Third, using mysql_error to find out if a certain record exists isn't the way to go. Better would be something along the lines of (pseudocode):
SELECT email FROM table WHERE email="someEmail"
if (rows found) {
alert "email already exists"
}
Finally, use mysqli or PDO.
Good luck learning webdevelopment!

Answer 3

Use:
window.location = "example.html";
See #Bart Friederichs's answer first, even if header works perfectly, the JavaScript alert wont work Because the page will be redirected once its completed and the browser will not execute the JavaScript for you.
<?php
print '<script type="text/javascript">';
print 'alert("The email address is already registered");';
print 'window.location = "register";';
print '</script>';
?>
You could also output it without PHP! for example:
if(strpos(mysql_error(),'Email')!==false)
{
?>
<script type="text/javascript">
alert("The email address is already registered");
window.location = "register.php";
</script>
<?php
}
?>