Mysql to Mysqli minimilistic adapter

mysql_adapter.php

<?php

if (! function_exists('mysql_connect')) {

	global $__link;

	function _link( $link = null ) {
		global $__link;

		if ( $link == null ) {
			$link = $__link;
		}

		return $link;
	}

	function mysql_connect( $host, $username, $password ) {
		global $__link;
		$__link = mysqli_connect( $host, $username, $password );

		return $__link;
	}

	function mysql_select_db( $database, $link = null ) {
		return mysqli_select_db( _link( $link ), $database );
	}

	function mysql_query( $sql, $link = null ) {
		return mysqli_query( _link( $link ), $sql );
	}

	function mysql_error( $link = null ) {
		return mysqli_error( _link( $link ) );
	}

	function mysql_free_result( $res ) {
		mysqli_free_Result( $res );
	}

	function mysql_get_server_info( $link = null ) {
		return mysqli_get_server_info( _link( $link ) );
	}

	function mysql_fetch_assoc( $res ) {
		return mysqli_fetch_assoc( $res );
	}

	function mysql_num_fields( $res ) {
		return mysqli_num_fields( $res );
	}

	function mysql_fetch_field( $res, $offset = 0 ) {

		$offset ++; // at least one iteration

		for ( $i = 0, $datum = null; $i < $offset; $i ++ ) {
			$datum = mysqli_fetch_field( $res );
		}

		return $datum;
	}

}