Twitter API Error using variables within php DEFINE - php

Question

I'm trying to pass a username and password variable to the twitter credentials but it keeps returning that I'm not authenticated. However, when I use the actual username and password, instead of the variables, it successfully authorizes.
$username = $_POST["username"];
$password = $_POST["password"];
$url = "http://search.twitter.com/search.atom?q=golf&show_user=true&rpp=100";
$search = file_get_contents($url);
$regex_name = '/\<name\>(.+?) \(/';
preg_match_all($regex_name,$search,$user);
for($i=0;$user[1][$i];$i++)
{
$follow = $user[1][$i];
define('TWITTER_CREDENTIALS', '$username:$password');
$url = "http://twitter.com/friendships/create/".$follow.".xml";
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL,$url);
curl_setopt($ch, CURLOPT_POST, 1);
curl_setopt($ch, CURLOPT_USERPWD, TWITTER_CREDENTIALS);
$result= curl_exec ($ch);
curl_close ($ch);
I'm thinking it has something to do with the colon in between the username and password, or perhaps trying to use variables within define function.
Any clues?

Answer 1

$username = $_POST["username"];
$password = $_POST["password"];
// INCORRECT. Will literary assign TWITTER_CREDENTIALS as $username:$password
// define('TWITTER_CREDENTIALS', '$username:$password');
// CORRECT, will parse the variables and assign the result to TWITTER_CREDENTIALS
define('TWITTER_CREDENTIALS', "$username:$password");
Remember strings with double quotes (") parse variables in the string, strings with single quotes (') do not.
Read more about strings in PHP:
PHP strings
Variable parsing in PHP strings
PHP string functions

Answer 2

it has something to do with using single quotes instead of double quotes.

Answer 3

You are using define inside a loop, that´s not gonna work because you can only define e constant once.