Difftime returns 0 all the time

Question

At the beginning I want to highlight that I've already read all similar posts in stack overflow. And nothing helped me.

#include <stdio.h>
#include <stdlib.h>
#define _USE_32BIT_TIME_T 1
#include <time.h>

int main(void)
{
  struct tm beg;
  struct tm aft;
  beg.tm_hour=0; beg.tm_min=0; beg.tm_sec=0;
  aft.tm_hour=11; aft.tm_min=19; aft.tm_sec=19;
  long long c;
  c=difftime(mktime(&aft),mktime(&beg));
  printf("%lld",c);
  return 0;
 }

It all the timr print out 0 an nothing else, but when I tried to change mktime(&aft) to time now time(&now) I got non-zero result. What should I correct in this code?

Answer 1

If the argument passed to mktime references a date before midnight, January 1, 1970, or if the calendar time cannot be represented, the function returns –1 cast to type time_t. (http://msdn.microsoft.com/en-us/library/aa246472(v=vs.60).aspx)

This could be causing the mktime to fail because the tm_year variable in beg and aft are invalid.

Setting this variable to a value that represents a year after 1970 produced the intended result.

#include <stdio.h>
#include <stdlib.h>
#define _USE_32BIT_TIME_T 1
#include <time.h>

int main(void)
{
    struct tm beg = {0};
    struct tm aft = {0};

    beg.tm_hour=0; beg.tm_min=0; beg.tm_sec=0;
    beg.tm_year = 71;  //Set to 1971

    aft.tm_hour=11; aft.tm_min=19; aft.tm_sec=19;
    aft.tm_year = 71;  //Set to 1971

    long long c;
    c=difftime(mktime(&aft),mktime(&beg));
    printf("%lld",c);
        return 0;
}