C#二个相减怎么获得天数，就是比如201225 与201231之间相差的天数

DateTime d1 =new DateTime(2004,1,1,15,36,05);
DateTime d2 =new DateTime(2004,3,1,20,16,35);
TimeSpan d3 = d2.Subtract(d1);
LbTime.Text = "相差:"
+d3.Days.ToString()+"天"
+d3.Hours.ToString()+"小时"
+d3.Minutes.ToString()+"分钟"
+d3.Seconds.ToString()+"秒";
法二、使用Sql中的DATEDIFF函数
使用方法：DATEDIFF ( datepart , startdate , enddate )
它能帮你取出你想要的各种形式的时间差，如相隔多少天，多少小时，多少分钟等，具体格式如下：

日期部分缩写

year	yy, yyyy
quarter	qq, q
Month	mm, m
dayofyear	dy, y
Day	dd, d
Week	wk, ww
Hour	hh
minute	mi, n
second	ss, s
millisecond	ms

如：datediff(mi,DtOpTime,DtEnd) 便能取出他们之间时间差的分钟总数，已经帮你换算好了，对于要求规定单位，时、分、秒特别有用

追加：datediff第一个参数就是比较两个时间的哪个部分，比如年，月，天等等。参数的缩写在上面的表中。

我的例子：

protected void rp_GroupInfo_ItemDataBound(object sender, RepeaterItemEventArgs e)
        {
            if (e.Item.ItemType == ListItemType.AlternatingItem || e.Item.ItemType == ListItemType.Item)
            {
                Repeater rp_Theme = (Repeater)e.Item.FindControl("rp_Theme");
                Label labgroupId = (Label)e.Item.FindControl("labgroupId");
                var pageInfo = new PageInformation
                {
                    PageSize = 6,
                    CurrentPage = ConvertHelper.ToInt32(Request.QueryString["page"], 1)
                };
                var themequery = ThemeBll.getByGroupID(System.Guid.Parse(labgroupId.Text),pageInfo);
                rp_Theme.DataSource = themequery;
                rp_Theme.DataBind();

                int icount = rp_Theme.Items.Count;
                for (int i = 0; i < icount; i++)
                {
                    Label labTime = (Label)rp_Theme.Controls[i].FindControl("labTime");
                    DateTime dtTime = Convert.ToDateTime(labTime.Text);
                    System.TimeSpan dtspanTime = DateTime.Now - dtTime;
                    if (dtspanTime.Days != 0)
                    {
                        labTime.Text = dtspanTime.Days.ToString() + "天" + dtspanTime.Hours.ToString() + "时" + dtspanTime.Minutes.ToString() + "分钟前";
                    }
                    if (dtspanTime.Days == 0 && dtspanTime.Hours != 0)
                    {
                        labTime.Text = dtspanTime.Hours.ToString() + "时" + dtspanTime.Minutes.ToString() + "分钟前";
                    }
                    if (dtspanTime.Hours == 0 && dtspanTime.Days == 0)
                    {
                        labTime.Text = dtspanTime.Minutes.ToString() + "分钟前";
                    }
                }
            }
        }