system/Router/Router.php
protected function setDefaultController()
	{
		if (empty($this->controller))
		{
			throw RouterException::forMissingDefaultRoute();
		}

		// Is the method being specified?
		if (sscanf($this->controller, '%[^/]/%s', $class, $this->method) !== 2)
		{
			$this->method = 'index';
		}

		if (! is_file(APPPATH . 'Controllers/' . $this->directory . ucfirst($class) . '.php'))
		{
			return;
		}

		$this->controller = ucfirst($class);

		log_message('info', 'Used the default controller.');
	}
protected function setDefaultController()
	{
		if (empty($this->controller))
		{
			throw RouterException::forMissingDefaultRoute();
		}

		// Is the method being specified?
		if (sscanf($this->controller, '%[^/]/%s', $class, $this->method) !== 2)
		{
			$this->method = 'index';
		}

		if (! is_file(APPPATH . 'Controllers/' . $this->directory . ucfirst($class) . '.php'))
		{
			return;
		}

		$this->controller = ucfirst($class);

		log_message('info', 'Used the default controller.');
	}
Sets the default controller based on the info set in the RouteCollection.