#include <stdio.h>
#include <time.h>
/**
* @brief Calculates the number of seconds between two struct tm date/time values.
*
* @param start Pointer to the starting struct tm.
* @param end Pointer to the ending struct tm.
* @return double The difference in seconds (end - start), or -1.0 on error.
*/
double get_seconds_between_2_dates(struct tm *start, struct tm *end) {
// Create local copies because mktime modifies the struct tm in place
struct tm start_copy = *start;
struct tm end_copy = *end;
// Convert struct tm representations to time_t (calendar time in seconds since epoch)
time_t start_time = mktime(&start_copy);
time_t end_time = mktime(&end_copy);
// Validate that conversion was successful
if (start_time == (time_t)(-1) || end_time == (time_t)(-1)) {
fprintf(stderr, "Error: Failed to normalize date structures.\n");
return -1.0;
}
// Use difftime to reliably calculate the difference in seconds across different systems
return difftime(end_time, start_time);
}
int main(void) {
// Initialize start date: October 27, 2026, 12:00:00
struct tm start_date = {0};
start_date.tm_year = 2026 - 1900; // Years since 1900
start_date.tm_mon = 10 - 1; // Months since January (0 to 11)
start_date.tm_mday = 27; // Day of the month (1 to 31)
start_date.tm_hour = 12; // Hours (0 to 23)
start_date.tm_min = 0; // Minutes (0 to 59)
start_date.tm_sec = 0; // Seconds (0 to 60)
start_date.tm_isdst = -1; // Let mktime determine daylight saving time status
// Initialize end date: October 27, 2026, 12:05:30
struct tm end_date = {0};
end_date.tm_year = 2026 - 1900;
end_date.tm_mon = 10 - 1;
end_date.tm_mday = 27;
end_date.tm_hour = 12;
end_date.tm_min = 5;
end_date.tm_sec = 30;
end_date.tm_isdst = -1;
// Calculate seconds between the two dates
double total_seconds = get_seconds_between_2_dates(&start_date, &end_date);
if (total_seconds >= 0.0) {
printf("Start Date: 2026-10-27 12:00:00\n");
printf("End Date: 2026-10-27 12:05:30\n");
printf("Total Seconds Between: %.0f\n", total_seconds);
}
return 0;
}
/*
run:
Start Date: 2026-10-27 12:00:00
End Date: 2026-10-27 12:05:30
Total Seconds Between: 330
*/
