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how to compare the time stamps, get the latest time stamp and save  it ???

Posted on 2004-10-10
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Last Modified: 2012-05-05
Hi experts,

I have a column containing time stamps, I know column number, time stamps like the followings:

10/1/2004 17:09
10/2/2004 12:03
10/6/2004 16:07
10/10/2004 4:06
..
..
..
..
more time stamps are added each day.
My questions are:
1. how can I get the latest time and save(write) it to somewhere (a file) for next time comparing ?
2. how can I use this saved time stamp to compare with new time stamps and save this new latest time stamp for next time comparing ?

Thanks
0
Comment
Question by:justinY
  • 5
  • 3
9 Comments
 
LVL 30

Expert Comment

by:Axter
ID: 12273829
You can use difftime function to determine the latest time.
0
 
LVL 39

Expert Comment

by:itsmeandnobodyelse
ID: 12274297
Define a class like that:

class Date
{
    int date;  // hold date as yyyymmdd
public:
    Date(const string& date);
    bool operator < (const Date& dt) { return date < dt.date; }
};

Convert your string date using the constructor. Compare dates by using '<', e. g.

   Date d1("10/06/2004");
   Date d2("04/04/2004");

   Date minDate = d1;
   if (d2 < d1)
        minDate = d2;

Regards, Alex
0
 
LVL 39

Expert Comment

by:itsmeandnobodyelse
ID: 12274307
And for timestamps:

class DateTime
{
    int date;  // hold date as yyyymmdd
    int time;  // hold time as hhmmss
public:
    DateTime(const string& datetime);
    bool operator < (const DateTime& dt)
      { return (date < dt.date) || (date == dt.date && time < dt.time); }
};

Convert your string datetime using the constructor. Compare timestamps by using '<', e. g.

   DateTime dt1("10/06/2004 10:03:20");
   DateTime dt2("04/04/2004 12:04:33");

   DateTime lastStamp = dt1;
   if (dt1 < dt2)
        lastStamp = dt2;


Regards, Alex

0
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Author Comment

by:justinY
ID: 12282970
Thanks Alex,
then my question is how can I get the latest timestamp from 2000 records ?
0
 
LVL 39

Expert Comment

by:itsmeandnobodyelse
ID: 12285676
Have a loop reading all records to a string and/or struct (depending on text or binary format of your input data), extract the date from the record, build a DateTime object and compare it to the last DateTime object til now. If the current DateTime is greater store it as new maximum.

       ifstream ifs("myfile.txt");
       string line;
       DateTime lastDt("01/01/1900 00:00:00");  
       while (ifs)
       {
             getline(ifs, line);
             if (ifs.fail()) break;
             // assume date/time is first two columns separated by ' '
             size_t pos = line.find(' ');
             if ((pos == string::npos)
                  return 1; // error
             pos = line.find(' ', pos+1);
             if ((pos == string::npos)
                  return 1; // error
             DateTime curDt(line.substr(0, pos));
             if (lastDt < curDt)
                 lastDt = curDt;
       }

Tell me if you need help with DateTime::DateTime(const string& dt).

Regards, Alex
     
0
 
LVL 39

Expert Comment

by:itsmeandnobodyelse
ID: 12285689
Correction:   if ((pos == string::npos) is wrong, remove the first opening bracket.


                 
0
 

Author Comment

by:justinY
ID: 12290693
Thanks Alex, but two questions come up:

1. I need to convert the date and time format to yyyymmddhhmm, how do i do that ?
2. I saved last latest timestamp to a file, then when I use to to compare this time, how do I call this file?
0
 
LVL 39

Accepted Solution

by:
itsmeandnobodyelse earned 500 total points
ID: 12296736
To 1)

Here is a constructor that takes a string containing both a date and time
in a format  similar to MM/DD/YYYY hh:mm:ss.

It takes any delimiter (but only one character) and single digits for day/month/hour. You may omit seconds, minutes, ....

class DateTime
{
    int date;  // hold date as yyyymmdd
    int time;  // hold time as hhmmss
public:
    DateTime(const string& datetime);
    bool operator < (const DateTime& dt)
      { return (date < dt.date) || (date == dt.date && time < dt.time); }
    friend ostream& operator<<(ostream& os, const DateTime& dt)
    {
        int y = dt.date/10000;
        int m = (dt.date%10000)/100;
        int d = dt.date%100;
        int h = dt.time/10000;
        int mi= (dt.time%10000)/100;
        int s = dt.time%100;
        os << m << '/' << d << '/' << y << ' ' << h;
        if (mi < 10)
            os << ":0" << mi;
        else
            os << ':' << mi;
        if (s > 0)
        {
            if (s < 10)
               os << ":0" << s;
            else
               os << ':' << s;
        }
        return os;
    }
};

DateTime::DateTime(const string& strdt)
{
    // expect something like "7/31/2000 21:05"
    int d   = 0;
    int m  = 0;
    int y   = 0;
    int h   = 0;
    int mi = 0;
    int s    = 0;
    enum { month, day, year, hour, minute, second, maxunits };
    int* dtu[maxunits] = { &m, &d, &y, &h, &mi, &s };
    int  idx = month;
    char c;
   
    for (int i = 0; i < strdt.length(); ++i)
    {
        c = strdt[i];
        if (isdigit(c))
            *dtu[idx] = (*dtu[idx]) * 10 + (c - '0');
        else
            idx++;
    }
    date = y*10000 + m*100 +  d;
    time = h*10000 + mi*100+ s;
}



To 2)
       string strdt;
       ifstream ifd("lastdate.txt");
       if (!ifd)
           return;  // error
       getline(ifd, strdt);      
       if (!ifd)
           return;  // error
       ifd.close();

       ifstream ifs("myfile.txt");
       string line;
       DateTime lastDt(strdt);  
       while (ifs)
       {
             getline(ifs, line);
             if (ifs.fail()) break;
             // assume date/time is first two columns separated by ' '
             size_t pos = line.find(' ');
             if ((pos == string::npos)
                  return 1; // error
             pos = line.find(' ', pos+1);
             if ((pos == string::npos)
                  return 1; // error
             DateTime curDt(line.substr(0, pos));
             if (lastDt < curDt)
                 lastDt = curDt;
       }

       ofstream ofs("lastdate.txt");
       ofs << lastDt << endl;
       ofs.close();

Regards, Alex

0
 

Author Comment

by:justinY
ID: 12302942
Thank you very much Alex.
0

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