CodeIgniter run library before database settings - codeigniter

Question

I test my Codeigniter site on localhost then update it on a server. Switching between them involves a lot of adjustment-related problems.
So I want to config it by only one constant: MYCUSTOM_SERVER_LOCATION
Then my database connection and password is configured according to location of my server(localhost or myhost). The only problem is that database.php is run before mysettings library. Even doing settings in a config file instead of a library has the same result.
[UPDATED]
application/config/autoload.php:
...
$autoload['libraries'] = array('mysettings','database','session');
...
application/libraries/mysettings.php:
<?php if ( ! defined('BASEPATH')) exit('No direct script access allowed');
define("MYCUSTOM_SERVER_LOCATION", "localhost");
class mysettings {
//////////////////////////////////////////////////
// option: localhost
// option: 000webhost
//$config["mycustom_server"]="localhost";
}
application/config/database.php
if(MYCUSTOM_SERVER_LOCATION=="localhost")
{
$db['default']['hostname'] = 'localhost';
$db['default']['username'] = '...';
$db['default']['password'] = '...';
$db['default']['database'] = '...';
}
else if(MYCUSTOM_SERVER_LOCATION=="myserver")
{
$db['default']['hostname'] = '...';
$db['default']['username'] = '...';
$db['default']['password'] = '...';
$db['default']['database'] = '...';
}
else
{
echo "Unknown server.";
}
output result:
A PHP Error was encountered
Severity: Notice
Message: Use of undefined constant MYCUSTOM_SERVER_LOCATION - assumed 'MYCUSTOM_SERVER_LOCATION'
Filename: config/database.php
Line Number: 51
A PHP Error was encountered
Severity: Notice
Message: Use of undefined constant MYCUSTOM_SERVER_LOCATION - assumed 'MYCUSTOM_SERVER_LOCATION'
Filename: config/database.php
Line Number: 58
Unknown server.

Answer 1

You can set the $active_group variable in application/config/database.php
Example Usage:
/*
The $active_group variable lets you choose which connection group to
make active. By default there is only one group (the 'default' group).
*/
$active_group = "development";
$db['development']['hostname'] = "localhost";
$db['development']['username'] = "us";
$db['development']['password'] = "";
$db['development']['database'] = "db1";