Here's a rough and ready solution that'll do the trick. I've left out reading the strings from the file, which sounds like you can do. Error-checking has also mostly been left out, since this uses hardcoded data.
#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <time.h>
void parse_time(char * ics_string, struct tm * dest_tm) {
char year[5], month[3], day[3], hour[3], minute[3], second[3];
sscanf(ics_string, "%4s%2s%2s%*1s%2s%2s%2s",
year, month, day, hour, minute, second);
dest_tm->tm_year = strtol(year, NULL, 10) - 1900;
dest_tm->tm_mon = strtol(month, NULL, 10) - 1;
dest_tm->tm_mday = strtol(day, NULL, 10);
dest_tm->tm_hour = strtol(hour, NULL, 10);
dest_tm->tm_min = strtol(minute, NULL, 10);
dest_tm->tm_sec = strtol(second, NULL, 10);
dest_tm->tm_isdst = -1;
if ( mktime(dest_tm) < 0 ) {
fprintf(stderr, "Couldn't get local time.\n");
exit(EXIT_FAILURE);
}
}
bool same_day(struct tm * first, struct tm * second) {
if ( (first->tm_year == second->tm_year) &&
(first->tm_mon == second->tm_mon) &&
(first->tm_mday == second->tm_mday) ) {
return true;
} else {
return false;
}
}
void calc_diff_string(char * buffer, size_t len,
struct tm * start_tm, struct tm * end_tm) {
char start_buffer[len];
char end_buffer[len];
strftime(start_buffer, len, "%B %d, %Y (%a), %I:%M %p", start_tm);
if ( same_day(start_tm, end_tm) ) {
strftime(end_buffer, len, "%I:%M %p", end_tm);
} else {
strftime(end_buffer, len, "%B %d, %Y (%a), %I:%M %p", end_tm);
}
sprintf(buffer, "%s to %s", start_buffer, end_buffer);
}
void print_time_diff(char * start_time, char * end_time) {
struct tm start_tm, end_tm;
char buffer[1024];
parse_time(start_time, &start_tm);
parse_time(end_time, &end_tm);
calc_diff_string(buffer, sizeof(buffer), &start_tm, &end_tm);
puts(buffer);
}
int main(void) {
print_time_diff("20131023T190000", "20131023T220000");
print_time_diff("20131023T190000", "20131024T220000");
return EXIT_SUCCESS;
}
which outputs:
paul@local:~/src/c/scratch/timestrip$ ./timestrip
October 23, 2013 (Wed), 07:00 PM to 10:00 PM
October 23, 2013 (Wed), 07:00 PM to October 24, 2013 (Thu), 10:00 PM
paul@local:~/src/c/scratch/timestrip$
Brief commentary:
parse_time()
takes a string in your format (excluding theDTSTART:
andDTEND:
prefixes) and populates astruct tm
with the corresponding time.same_day()
returnstrue
if the two times are on the same day, so you get the short-form message in the output.calc_diff_string()
calculates your output string.print_time_diff()
glues them all together and outputs your string.