C#正则匹配问题---------------------bbs-listbymodel.aspx?forumid=47

string str = "bbs_listbymodel.aspx?forumid=4748&cd=0&"
+ "bbs_listbymodel.aspx?forumid=4747&cd=0&l"
+ "bbs_listbymodel.aspx?forumid=4746&cd=0&l"
+ "bbs_listbymodel.aspx?forumid=4745&cd=0&l"
+ "bbs_listbymodel.aspx?forumid=4744&cd=0&l"
+ "bbs_listbymodel.aspx?forumid=4743&cd=0&l";
string result="";
Regex reg = new Regex(@"forumid=(?\d{4})");
MatchCollection mats = reg.Matches(str);
foreach (Match mat in mats)
{
result=mat.Groups["id"].Value;//这里取匹配到的值,怎么处理看你自己了
}