php得到客户ip地址

从一些CMS函数库中提取出来的函数，可以得到访问客户的IP，其方法都是大同小异

function getip()
{
	if(getenv('HTTP_CLIENT_IP') && strcasecmp(getenv('HTTP_CLIENT_IP'), 'unknown'))
	{
		$onlineip = getenv('HTTP_CLIENT_IP');
	}
	elseif(getenv('HTTP_X_FORWARDED_FOR') && strcasecmp(getenv('HTTP_X_FORWARDED_FOR'), 'unknown'))
	{
		$onlineip = getenv('HTTP_X_FORWARDED_FOR');
	}
	elseif(getenv('REMOTE_ADDR') && strcasecmp(getenv('REMOTE_ADDR'), 'unknown'))
	{
		$onlineip = getenv('REMOTE_ADDR');
	}
	elseif(isset($_SERVER['REMOTE_ADDR']) && $_SERVER['REMOTE_ADDR'] && strcasecmp($_SERVER['REMOTE_ADDR'], 'unknown'))
	{
		$onlineip = $_SERVER['REMOTE_ADDR'];
	}
	return $onlineip;
}