C#实现的一些常见时间格式

string aa = datetime.now.toshortdatestring();//"2019/9/23"
string bb = datetime.now.toshorttimestring();//"上午 10:21"
string ff = datetime.now.tolongdatestring();//2019年9月23日
string gg = datetime.now.tolongtimestring();//上午 10:22:07

int monthdays = datetime.daysinmonth(datetime.now.year, datetime.now.month);//获取某月在某年中的天数

datetime from = datetime.parseexact(/*tdfrom.text*/"201909", "yyyymm", datetimeformatinfo.invariantinfo);//输入的string转datetime
datetime end = datetime.parseexact(/*tdend.text*/"201909", "yyyymm", datetimeformatinfo.invariantinfo);

string nian = datetime.now.tostring("y");//2019年9月
string nian1 = datetime.now.tostring("y");//2019年9月

string y1 = datetime.now.tostring("r");//mon, 23 sep 2019 10:31:48 gmt
string y2 = datetime.now.tostring("r");//mon, 23 sep 2019 10:32:10 gmt

string xingqiji = datetime.now.tostring("dddd");// "星期一"
string zhouji = datetime.now.tostring("ddd");//  "周一"
string ri = datetime.now.tostring("dd");// 23
string ershisi = datetime.now.tostring("hh"); //3
string shier = datetime.now.tostring("hh");//15

string chang = datetime.now.tostring("f");//2019年9月23日 上午 10:34:08
string chang1 = datetime.now.tostring("f");//2019年9月23日 上午 10:34
string cahng2 = datetime.now.tostring("g");//2019/9/23 上午 10:35:07
string cahng3 = datetime.now.tostring("g");//2019/9/23 上午 10:35
string cahng4 = datetime.now.tostring("d");//2019年9月23日
string cahng5 = datetime.now.tostring("d");//2019/9/23

string now = datetime.now.tostring("yyyy/mm/dd hh:mm:ss");//2019/09/23 10:14:54
string a = datetime.now.addyears(20).tostring("yyyy/mm/dd hh:mm:ss");//2039/09/23 10:14:54
string b = datetime.now.addmonths(-2).tostring("yyyy/mm/dd hh:mm:ss");//"2019/07/23 10:14:54"
string c = datetime.now.adddays(-8).tostring("yyyy/mm/dd hh:mm:ss");//"2019/09/15 10:14:54"
string d = datetime.now.addhours(24).tostring("yyyy/mm/dd hh:mm:ss");//"2019/09/24 10:14:54"
string f = datetime.now.addminutes(1440).tostring("yyyy/mm/dd hh:mm:ss");//2019/09/24 10:14:54
string g = datetime.now.addseconds(3600).tostring("yyyy/mm/dd hh:mm:ss");//2019/09/23 11:14:54"
string h = datetime.now.addseconds(3600).tostring("yyyy/mm/dd hh:mm:ss:ffff");//2019/09/23 11:14:54:7992