mktime() and difftime() problem

[mynicks]

Two questions please.

1. can someone read the code and help me see why the code is not giving a correct answer? To test the code i set an easy value as the date of birth,i set it one day before today, on second try i set it a decade ago but still wrong result. I get a 0 value (or a wrong int number if i mess a lot with the code). The code is an example from a textbook. I know there are other ways to do it, but i do not want to use other functions only these two: mktime,difftime if there is a way...

2.I checked the mktime() example on this forum and it says tm_year= myvalue -1900. I think that the epoch is 1970 not 1900 or... it is 1900 the default value exclusively for struct tm? What am i missing/ignoring here?

i am using windows 10.

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


int main(void)
{
     time_t date;
	 struct tm birth = {0};

	 printf("you were born in...(the format is :yy/mm/dd): ");
	 fflush(stdout);
	 scanf( "%d %d %d", &birth.tm_year, &birth.tm_mon, &birth.tm_mday );
	 birth.tm_year -= 1900; //why not 1970? epoch= 1970! right?	
	 birth.tm_mon -= 1;
	 date = mktime(&birth);
	 printf("your age in seconds is:: \n %ld", difftime(time(NULL),date)); 
}

Thanks for your feedback, if any.

[jlb]

You appear to be using the wrong format specifier for the value returned by difftime(). The "%ld" specifier is for a long int, difftime() returns a double not a long int.

[mynicks]

i changed it from integer to float, i get a better result 95% correct, but i think it is a bit off the correct answer by 30 minutes. To test the code, i set it one day before today and then i made the subtraction 86400 - 84500 = 1900 seconds( aka 0.523 hours which is 30 mins)

(The moment i tested the value the program is giving is 84500) .

As the time goes by the 84500 is slowly increasing to eventually become equal to 86400. I do not know what i am missing but that 84500 is not the exact answer. In my gmt+3 time here this moment i type this message the 84500 will become equal to 86400 at 01:15 after midnight, which does not make a lot of sense to me....

[jlb]

i changed it from integer to float, i get a better result 95% correct,

Changed what from an integer to a float?

Post your modified code.

[mynicks]

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


int main(void)
{
     time_t date;
	 struct tm birth = {0};

	 printf("you were born in...(the format is :yy/mm/dd): ");
	 fflush(stdout);
	 scanf( "%d %d %d", &birth.tm_year, &birth.tm_mon, &birth.tm_mday );
	 birth.tm_year -= 1900; //why not 1970? epoch= 1970! right?
	 birth.tm_mon -= 1;
	 date = mktime(&birth);
	 printf("your age in seconds is:: \n %f", difftime(time(NULL),date));
}

and this works fine

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


int main(void)
{
     time_t date;
	 struct tm birth = {0};

	 printf("you were born in...(the format is :yy/mm/dd): ");
	 fflush(stdout);
	 scanf( "%d %d %d", &birth.tm_year, &birth.tm_mon, &birth.tm_mday );
	 birth.tm_year -= 1900; //why not 1970? epoch= 1970! right?
	 birth.tm_mon -= 1;
	 date = mktime(&birth);
	 printf("your age in seconds is:: \n %ld", (long int)difftime(time(NULL),date));
}