Need Help Programming in C comparing times together..

Answer 1

There is an example of making a time here. You can then compare the times with the difftime method.

Answer 2

If it were me, I'd be tempted to just save the result of time() to the file. That would save a whole lot of string parsing work on the other side.

Answer 3

Paring your format is easy in C. Use this to read the time components from the file:

int hr, min; 
fscanf (file, "%d:%d", &hr, &min);

Here is a complete solution:

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

struct HrMin_ {
  int hr;
  int min;
};
typedef struct HrMin_ HrMin;

static const double TIME_DIFFERENCE = (double) (5 * 1000);

static HrMin read_time (FILE* file);

int
main (int argc, char **argv)
{
  time_t sys_time_t = 0;
  struct tm *sys_time = NULL;
  struct tm *file_time = NULL;
  double d = 0.0f;

  if (argc != 2)
    {
      printf ("Usage: time_cmp <time_file>\n");
      return 1;
    }

  time (&sys_time_t);

  sys_time = localtime (&sys_time_t);
  file_time = malloc (sizeof (struct tm));

  file_time->tm_sec = sys_time->tm_sec;
  file_time->tm_min = sys_time->tm_min;
  file_time->tm_hour = sys_time->tm_hour;
  file_time->tm_mday = sys_time->tm_mday;
  file_time->tm_mon = sys_time->tm_mon;
  file_time->tm_year = sys_time->tm_year;
  file_time->tm_wday = sys_time->tm_wday;
  file_time->tm_yday = sys_time->tm_yday;
  file_time->tm_isdst = sys_time->tm_isdst;  

  FILE *file = fopen (argv[1], "r");
  if (file == NULL)
    {
      printf ("Failed to open file: %s\n", argv[1]);
      return 1;
    }
  HrMin hr_min = read_time (file);
  fclose (file);

  file_time->tm_hour = hr_min.hr;
  file_time->tm_min = hr_min.min;

  d = difftime (sys_time_t, mktime (file_time));
  free (file_time);

  if (d < 0) d *= -1;
  printf ("Diff: %f\n", d);
  if (d >= TIME_DIFFERENCE)
    printf ("WARN!\n");

  return 0;
}

static HrMin 
read_time (FILE *file)
{
  HrMin hr_min;
  hr_min.hr = 0;
  hr_min.min = 0;
  fscanf (file, "%d:%d", &hr_min.hr, &hr_min.min);
  return hr_min;
}