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date calculation

Posted on 2003-03-10
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Last Modified: 2012-05-04

I am trying to get diffrance between in two dates.

Start Date/Time :  yyyy-mm-dd hh:mm:ss.t

End Date/Time :   yyyy-mm-dd hh:mm:ss.t


What is the best way to calculate diffrance in seconds or minutes?.

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Question by:raza
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7 Comments
 
LVL 1

Expert Comment

by:jcaldwel
ID: 8107436

In time.h...
    extern double       difftime(time_t, time_t);
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Author Comment

by:raza
ID: 8109239

I have string value in yyyy-mm-dd hh:mm:ss.t format

how do I use time_t for the input of difftime?
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LVL 2

Expert Comment

by:constructor
ID: 8109544
Fill your secs, mins, hours, days etc into a tm struct (also in time.h), then call mktime on it, which returns the time_t you want for difftime...
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Author Comment

by:raza
ID: 8109886

The following is a code I am trying to get it work. I am always getting 0 for difftime;



static int DiffDateTime(
     char *EndDateTime,
     char *StartDateTime
     )
{
     /*
      * Input DateTime format
      * y y y y - m m - d d   h h : m m : s s.t
      * 1 2 3 4 5 6 7 8 9 0 1 1 2 3 4 5 6 7 8
      */

     char StringVal[32];

     struct tm Start;
     struct tm End;

     PARS_mid(StartDateTime,0,4,StringVal);
     Start.tm_year = atoi(StringVal);
     
     PARS_mid(StartDateTime,5,2,StringVal);
     Start.tm_mon  = atoi(StringVal);
     
     PARS_mid(StartDateTime,8,2,StringVal);
     Start.tm_mday  = atoi(StringVal);

     PARS_mid(StartDateTime,11,2,StringVal);
     Start.tm_hour  = atoi(StringVal);
     
     PARS_mid(StartDateTime,14,2,StringVal);
     Start.tm_min  = atoi(StringVal);

     PARS_mid(StartDateTime,17,2,StringVal);
     Start.tm_sec  = atoi(StringVal);
     

     PARS_mid(EndDateTime,0,4,StringVal);
     End.tm_year  = atoi(StringVal);
     
     PARS_mid(EndDateTime,5,2,StringVal);
     End.tm_mon  = atoi(StringVal);
     
     PARS_mid(EndDateTime,8,2,StringVal);
     End.tm_mday  = atoi(StringVal);

     PARS_mid(EndDateTime,11,2,StringVal);
     End.tm_hour  = atoi(StringVal);
     
     PARS_mid(EndDateTime,14,2,StringVal);
     End.tm_min  = atoi(StringVal);

     PARS_mid(EndDateTime,17,2,StringVal);
     End.tm_sec  = atoi(StringVal);
     
     return difftime(mktime(&End),mktime(&Start));

}




static char *PARS_mid (
                            const char *chString, /* String             */
                            int start,      /* Starting Possition */
                            int len,           /* lenth of string    */
                         char       *result
                            )
{
     int i;
     int k;
     int nActualEnd;
     int nActualStart;
     int nIndex;


     if(!strlen(chString))                         /* If There Is No The Length                            */
          return NULL;                              /* Return NULL                                                */

     if ( (unsigned int) start > strlen(chString))               /* Make Sure The Start Is Not More Than The Length */
          return NULL;                              /* If It Is Return Null                                      */
     if (start < 0)                                   /* If The Start Is Less Than 0                            */
          nActualStart = 0;                         /* Set The nActualStart To 0                            */
     else          
          nActualStart = start;                    /* Else Set The nActualStart                            */

     if ( (unsigned int) len > strlen(chString))                    /* If The Length Is Longer Than The String             */
          nActualEnd = strlen(chString);          /* Set The nActualEnd To The Length Of The String  */
     else          
          nActualEnd = len;                         /* Else nActualEnd To The Length                       */

     /* Copy The Part We Want From The Orginal String To The Result */
     
     for (i = 0, nIndex = nActualStart, k = 0; i < nActualEnd; i++)    
     {          
          if (chString[nIndex] != '\0')               /* If Not A NULL Char */
               result[k++] = chString[nIndex++];
          else
               break;
     }

     result[k] = '\0';                              /* Add A NULL Char To The End Of The String */

    return result;                                   /* Return The New String */

}
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LVL 2

Accepted Solution

by:
constructor earned 200 total points
ID: 8110307
It is good practice to zero out structures before use (since you only specify some of the fields). And the year field in struct tm is counted from 1900, so you have to subtract this number later. Moreover, difftime returns a double, so you have to cast explicitly, or change your function to return a double. Here is how it probably should look:

static double DiffDateTime(const char *EndDateTime,const char *StartDateTime)
{
     /* Input format: 'yyyy-mm-dd hh:mm:ss' */
     char StringVal[32];
     struct tm Start,End;
     /* Make start time: */
     memset(&Start,0,sizeof(struct tm));
     PARS_mid(StartDateTime,0,4,StringVal);
     Start.tm_year=atoi(StringVal)-1900;
     PARS_mid(StartDateTime,5,2,StringVal);
     Start.tm_mon=atoi(StringVal);
     PARS_mid(StartDateTime,8,2,StringVal);
     Start.tm_mday=atoi(StringVal);
     PARS_mid(StartDateTime,11,2,StringVal);
     Start.tm_hour=atoi(StringVal);
     PARS_mid(StartDateTime,14,2,StringVal);
     Start.tm_min=atoi(StringVal);
     PARS_mid(StartDateTime,17,2,StringVal);
     Start.tm_sec=atoi(StringVal);
      /* Make end time: */
     memset(&End,0,sizeof(struct tm));
     PARS_mid(EndDateTime,0,4,StringVal);
     End.tm_year=atoi(StringVal)-1900;
     PARS_mid(EndDateTime,5,2,StringVal);
     End.tm_mon=atoi(StringVal);
     PARS_mid(EndDateTime,8,2,StringVal);
     End.tm_mday=atoi(StringVal);
     PARS_mid(EndDateTime,11,2,StringVal);
     End.tm_hour=atoi(StringVal);
     PARS_mid(EndDateTime,14,2,StringVal);
     End.tm_min=atoi(StringVal);
     PARS_mid(EndDateTime,17,2,StringVal);
     End.tm_sec=atoi(StringVal);
     /* Return */
     return (int)difftime(mktime(&End),mktime(&Start));
}


Here's a test program of mine, if you can't get the other to work:

#include <stdio.h>
#include <time.h>

/* Format: 'yyyy-mm-dd hh:mm:ss' */
const char datetime[]="2003-02-11 11:28:34";

time_t StringToTime(const char *s)
{
     struct tm t;

/*     if(ValidateString(s)==0) return -1; */
     memset(&t,0,sizeof(struct tm));
     sscanf(s,"%d",&t.tm_year);
     sscanf(s+5,"%d",&t.tm_mon);
     sscanf(s+8,"%d",&t.tm_mday);
     sscanf(s+11,"%d",&t.tm_hour);
     sscanf(s+14,"%d",&t.tm_min);
     sscanf(s+17,"%d",&t.tm_sec);
     t.tm_year-=1900;
     return mktime(&t);
}

int main()
{
     time_t thetime,curtime;

     thetime=StringToTime(datetime);
     time(&curtime);
     printf("\nInitial time: %s",ctime(&thetime));
     printf("Current time: %s",ctime(&curtime));
     printf("Difference:   %.0lf s\n",difftime(curtime,thetime));
     return 0;
}

You can make your own validation function if you need it...
0
 
LVL 2

Expert Comment

by:constructor
ID: 8110312
Ooops, I just did the opposite mix-up of you. The function head should of course read:

static int DiffDateTime(const char *EndDateTime,const char *StartDateTime)

or you should remove the cast to int again.
0
 

Author Comment

by:raza
ID: 8110479
Thank you very much... you have been very helpful.
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