Faster alternative to DateTime.ParseExact

c#, datetime, parsing

Solution

The idea of splitting the string is on the right track, but substring is slow. Whenever I split a string, I use the character accessor. yyyyMMddTHHmmssfff Disclaimer: T

public class DateParser1
{
    private static System.String DateFormat="yyMMddTHHmmssfff";

    public static System.DateTime GetDate(System.String SourceString, int Offset=0) // Offset eliminates need for substring
    {
        int Year=0;
        int Month=0;
        int Day=0;
        int Hour=0;
        int Minute=0;
        int Second=0;
        int HourOffset=0;
        int MS=0;
        if(SourceString.Length+Offset<DateFormat.Length) throw new System.Exception(System.String.Format("Date Too Short {0} For {0}",SourceString.Substring(Offset),DateFormat));
        for(int i=0;i<DateFormat.Length;i++)
        {
            System.Char c=SourceString[Offset+i];
            switch(DateFormat[i])
            {
                  case 'y':
                      Year=Year*10+(c-'0');
                      break;
                  case 'M':
                      Month=Month*10+(c-'0');
                      break;
                  case 'd':
                      Day=Day*10+(c-'0');
                      break;
                  case 'T':
                      if(c=='p'||c=='P')
                           HourOffset=12;
                      break;
                  case 'h':
                      Hour=Hour*10+(c-'0');
                      if(Hour==12) Hour=0;
                      break;
                  case 'H':

                      Hour=Hour*10+(c-'0');
                      HourOffset=0;
                      break;
                  case 'm':
                      Minute=Minute*10+(c-'0');
                      break;
                  case 's':
                      Second=Second*10+(c-'0');
                      break;
                  case 'f':
                      MS=MS*10+(c-'0');
                      break;
            }

        }
        if(Year>30) //Change For Your Business Rules
        {
               Year+=1900;
        }
        else
        {
               Year+=2000;
        }
        try
        {
            return new System.DateTime(Year,Month,Day,Hour+HourOffset,Minute,Second,MS);
        }
        catch(System.Exception)
        {
            throw new System.Exception(System.String.Format("Error In Date: {0}/{0}/{0} {0}:{0}:{0}.{0} - {0} {0}",Year,Month,Day,Hour+HourOffset,Minute,Second,MS,DateFormat,SourceString.SubString(Offset,DateFormat.Length)));
        }
    }
}

Problem

I parse a string into a DateTime millions of times: ``` public static CultureInfo ci = CultureInfo.InvariantCulture; while (!reader.EndOfStream) { line = reader.ReadLine(); string[] fields = line.Split(' '); DateTime newDT = DateTime.ParseExact(fields[0], "yyyyMMddTHHmmssfff", ci); } ``` My profiler highlights ParseExact as being a huge part of time taken. Is there any other method/approach that could parse the string into a DateTime that would be faster? FOLLOW UP1: 1) I tried this - but speed was same ``` bool OK = DateTime.TryParseExact(fields[0], "yyyyMMddTHHmmssfff", null, System.Globalization.DateTimeStyles.None,out DT); ``` 2) I tried to code my own parser - but this too was as slow: ``` public static DateTime fastParse(ref string s) { return new DateTime(int.Parse(s.Substring(0,4)), int.Parse(s.Substring(4,2)),int.Parse(s.Substring(6,2)), int.Parse(s.Substring(9,2)),int.Parse(s.Substring(11,2)),int.Parse(s.Substring(13,2)),int.Parse(s.Substring(15, 3))); } ``` FOLLOW UP2 I tried Master117 suggestion of storing values - AGAIN it is NO faster - perhaps the issue is the construction? ``` public class fastParseData { int year; int mon; int day; int hour; int min; string previousSlice = ""; public DateTime fastParse(ref string s) { if (previousSlice != s.Substring(0, 12)) { year=int.Parse(s.Substring(0,4)); mon=int.Parse(s.Substring(4,2)); day=int.Parse(s.Substring(6,2)); hour= int.Parse(s.Substring(9,2)); min = int.Parse(s.Substring(11,2)); previousSlice = s.Substring(0, 12); } return new DateTime(year, mon, day, hour,min, int.Parse(s.Substring(13, 2)), int.Parse(s.Substring(15, 3))); } } ``` FOLOW UP3 ``` public class fastParseData { int year; int mon; int day; int hour; int min; string previousSlice = ""; DateTime previousDT; public DateTime fastParse(ref string s) { if (previousSlice != s.Substring(0, 12)) { year=int.Parse(s.Substring(0,4)); mon=int.Parse(s.Substring(4,2)); day=int.Parse(s.Substring(6,2)); hour= int.Parse(s.Substring(9,2)); min = int.Parse(s.Substring(11,2)); previousSlice = s.Substring(0, 12); previousDT = new DateTime(year, mon, day, hour,min,0,0); } return previousDT.AddMilliseconds((int.Parse(s.Substring(13, 2))*1000)+int.Parse(s.Substring(15, 3))); } } ``` FOLLOW UP4 From my profiler the crux seems to be ``` int.Parse(s.Substring(13, 2)) ``` With the Parse bit being more costly than the substring. I tried ``` int.TryParse(s.Substring(13, 2),NumberStyles.None,ci, out secs) Convert.ToInt32(s.Substring(13, 2)); ``` but again - no difference in speed. Is there a faster way to parse an int?

Original source