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Top Forums Programming How to compare dates in C/C++ Post 302086887 by jim mcnamara on Monday 28th of August 2006 10:03:10 AM
Old 08-28-2006
1. convert the date (you pick the format) to seconds since the start of the era. use strptime and mktime.
2. compare the two time_t (seconds) values.
example using MON-DD-YYYY format:
Code:
#include <time.h>
time_t to_seconds(const char *date)
{
        struct tm storage={0,0,0,0,0,0,0,0,0};
        char *p=NULL;
        time_t retval=0;

        p=(char *)strptime(date,"%d-%b-%Y",&storage);
        if(p==NULL)
        {
                retval=0;
        }
        else
        {
                retval=mktime(&storage);
        }
        return retval;
}

int main()
{
   char *date1="20-JUN-2006";
   char *date2="21-JUN-2006";
   time_t d1=to_seconds(date1);
   time_t d2=to_seconds(date2);
   
   printf("date comparison: %s %s ",date1,date2);
   if(d1==d2) printf("equal\n");
   if(d2>d1)  printf("second date is later\n");
   if(d2<d1)  printf("seocnd date is earlier\n");
   return 0;
}

 

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OFFTIME(3)						   BSD Library Functions Manual 						OFFTIME(3)

NAME
offtime, timeoff, timegm, timelocal -- convert date and time LIBRARY
Standard C Library (libc, -lc) SYNOPSIS
#include <time.h> struct tm * offtime(const time_t * clock, long int offset); struct tm * offtime_r(const time_t * clock, long int offset, struct tm *ret); time_t timeoff(struct tm * tm, long int offset); time_t timegm(struct tm * tm); time_t timelocal(struct tm * tm); DESCRIPTION
These functions are inspired by C standard interfaces named similarly. offtime() converts the calendar time clock, offset by offset seconds, into broken-down time, expressed as Coordinated Universal Time (UTC). offtime_r() is similar to offtime() but it places the returned struct tm * in the user supplied ret argument. timeoff() converts the broken-down time tm, expressed as UTC, offset by offset seconds, into a calendar time value. timegm() converts the broken-down time tm into a calendar time value, effectively being the inverse of gmtime(3). It is equivalent to the C standard function mktime(3) operating in UTC. timelocal() converts the broken down time tm, expressed as local time, into a calendar time value. It is equivalent to the C standard func- tion mktime(3), and is provided for symmetry only. SEE ALSO
ctime(3), tm(3), tzset(3) BSD
April 14, 2011 BSD
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