gistfile1.txt

#define STB_DEFINE
#include "stb.h"

int get_seconds(char *timestamp)
{
   int sec;
   struct tm t;

   // sscanf was very slow
   t.tm_year = atoi(timestamp+ 0);
   t.tm_mon  = atoi(timestamp+ 5);
   t.tm_mday = atoi(timestamp+ 8);
   t.tm_hour = atoi(timestamp+11);
   t.tm_min  = atoi(timestamp+14);
   t.tm_sec  = atoi(timestamp+17);

   --t.tm_mon; // month format mismatch
   t.tm_year -= 1900;
   t.tm_isdst = 0; // bogus!
   sec = mktime(&t); // this will probably be slow as heck
   assert(sec != -1);
   return sec;
}

int main(int argc, char **argv)
{
   stb_sdict *d = stb_sdict_new(1);
   void *p;
   int i=0, len;
   char *s = stb_file("c:/x/data.txt", &len);
   for (i=0; i < len; i += 20+20+8+2) {
      int timesofar=0;
      int t0 = get_seconds(s+i);
      int t1 = get_seconds(s+i+20);
      char *id = s + i + 40;
      id[8] = '\0';

      timesofar = (int) stb_sdict_get(d, id);
      timesofar += (t1-t0);
      stb_sdict_set(d, id, (void *) timesofar);
   }
   free(s);

   // does the output need to be sorted? I don't know C# so can't tell
   stb_sdict_for(d,i,s,p) {
      printf("%s %d\n", s, (int) p);
   }
   return 0;
}