I am trying to convert the GMT time into unix epoch (starting from 1970), looks like there is a small bug
in code , i could not get and exhausted.
I see following difference
Non leap years
Expected output: Jan 20 19:00:01 2019 GMT = 1548010801
Actual output: 1548097201 (which is Jan 21 19:00:01 2019 GMT, 1 day difference)
Leap Year
Expected output: Dec 27 14:52:30 2020 GMT = 1609080750
Actual output: 1609253550 (which is Dec 29 14:52:30 2020 GMT, 2 days difference)
I really appreciate any help in finding the problem.
`
#include <stdio.h>
#include <string.h>
#include <time.h>
#define BASE_YEAR 1970
void print_time_readable_format(struct tm tm);
int convert_gmt_date_time_to_tm_format(char* gmt_time_fmt);
int check_year_is_leap_or_normal(int year);
int get_number_of_leap_years_from_base_year(int start_year, int end_year);
int convert_gmt_to_epoch(struct tm tm);
int main()
{
int epoch = 0;
//char gmt_time_fmt[] = "Jan 20 19:00:01 2019 GMT";
//char gmt_time_fmt[] = "Dec 27 14:52:30 2020 GMT";
char gmt_time_fmt[] = "Jan 01 00:00:00 1970 GMT";
epoch = convert_gmt_date_time_to_tm_format(gmt_time_fmt);
printf("time in GMT = %s and epoch is %d\n", gmt_time_fmt, epoch);
return 0;
}
int convert_gmt_date_time_to_tm_format(char* gmt_time_fmt)
{
struct tm tm;
char tm_time_fmt[255];
//set tm struture to 0
memset(&tm, 0, sizeof(struct tm));
// convert gmt_time_fmt to format required by 'tm' structure
strptime(gmt_time_fmt, "%B %d %H:%M:%S %Y GMT", &tm);
strftime(tm_time_fmt, sizeof(tm_time_fmt), "%s", &tm);
printf("tm_time_fmt = %s\n", tm_time_fmt);
print_time_readable_format(tm);
return convert_gmt_to_epoch(tm);
return 0;
}
int convert_gmt_to_epoch(struct tm tm)
{
int days_by_month [2][12] = {
/* normal years */
{ 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334},
/* leap years */
{ 0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335}
};
int current_year = tm.tm_year+1900;
printf("current_year =%d\n", current_year);
int total_years_passed = current_year - BASE_YEAR;
printf("total_years_passed =%d\n", total_years_passed);
int nleap_years_passed = get_number_of_leap_years_from_base_year(BASE_YEAR, current_year);
int normal_years = total_years_passed - nleap_years_passed;
printf("normal_years =%d\n", normal_years);
int total_days_passed = (normal_years*365 + nleap_years_passed*366 );
printf("total_days_passed =%d\n", total_days_passed);
total_days_passed += days_by_month[check_year_is_leap_or_normal(current_year)][tm.tm_mon];
printf("total_days_passed after adding month =%d\n", total_days_passed);
total_days_passed += tm.tm_mday;
printf("total_days_passed after adding day =%d\n", total_days_passed);
total_days_passed = total_days_passed*24 + tm.tm_hour;
total_days_passed = total_days_passed*60 + tm.tm_min;
total_days_passed = total_days_passed*60 + tm.tm_sec;
printf("total_days_passed final =%d\n", total_days_passed);
return total_days_passed;
}
int get_number_of_leap_years_from_base_year(int start_year, int end_year)
{
int leap_year_count = 0;
int year = start_year;
while( year <= end_year)
{
if(check_year_is_leap_or_normal(year))
leap_year_count++;
year++;
}
printf("leap_year_count = %d\n", leap_year_count);
return leap_year_count;
}
int check_year_is_leap_or_normal(int year)
{
if( ( year%4 == 0 ) && ( ( year%400 == 0 ) || ( year%100 != 0)))
return 1;
else
return 0;
}
void print_time_readable_format(struct tm tm)
{
printf("tm.tm_year = %d ", tm.tm_year);
printf("tm.tm_mon = %d ", tm.tm_mon);
printf("tm.tm_mday = %d ",tm.tm_mday);
printf("tm.tm_hour = %d ", tm.tm_hour);
printf("tm.tm_min = %d ", tm.tm_min );
printf("tm.tm_sec = %d\n", tm.tm_sec );
}
`