mktime() seg fault

Question

I am trying to add a week repeatedly to an event struct, which contains date information. I am doing this in order to create a multiple instances of an event up until a certain time. I'm getting a seg fault on my mktime function where full_time = mktime(&caltime); and I have no clue why.

void multiple(icalevent event, int is_location){
    icalevent temp;
    int rrule_bound = atoi(event.rrule);
    int rtime_bound = atoi(event.rtime);
    int start_bound = atoi(event.start);
    int stime_bound = atoi(event.stime);
    char buffer[9];
    struct tm caltime;
    time_t full_time;
    char time_str[15];

    temp = cpystruct(event, is_location); 
    while((start_bound <= rrule_bound) && (stime_bound <= rtime_bound)){
        memset(&caltime, 0, sizeof(struct tm));
        strncpy(time_str, temp.start, 9);
        strncat(time_str, temp.stime, 6);

        strptime(time_str, "%Y%m%d%H%M%S", &caltime);
        caltime.tm_mday += 7;
        full_time = mktime(&caltime);
        if(caltime.tm_isdst == 1){
            caltime.tm_hour -= 1;
        }
        full_time = mktime(&caltime);

        strftime(buffer, 9, "%Y%m%d", &caltime);
        start_bound = atoi(buffer);
        strncpy(temp.end, buffer, 8);
        strncpy(temp.start, buffer, 8);

        if((start_bound <= rrule_bound) && (stime_bound <= rtime_bound)){
            /*create a sort string*/

            calendar[percent_full] = cpystruct(temp, is_location);
            printst(calendar[percent_full]);
            percent_full++;
        }
        else{
            break;
        }

    }

    return;
    }

The icalevent structure:

    typedef struct{
        char start[9]; /*"YYYYMMDD*/
        char stime[7]; /*"HHMMSS"*/
        char end[9]; /*"YYYYMMDD"*/
        char etime[7]; /*"HHMMSS"*/
        char rrule[9]; /*"YYYYMMDD"*/
        char rtime[7]; /*"HHMMSS"*/
        char *location; /*"2343 fake street"*/
        char *summary; /*"Halloween party"*/
        char *sort_str; /*"YYYYMMDDHHMMSSHalloween party*/
     } icalevent

Edit:

icalevent cpystruct(icalevent temp, int is_location) {
    icalevent perm;
    strncpy(perm.start, temp.start, 9);
    strncpy(perm.stime, temp.stime, 7);
    strncpy(perm.end, temp.end, 9);
    strncpy(perm.etime, temp.etime, 7);
    strncpy(perm.rrule, temp.rrule, 9);
    strncpy(perm.rtime, temp.rtime, 7);
    if(is_location) {
        perm.location = strdup(temp.location);
    } else {
        perm.location = NULL;
    }

    perm.summary = strdup(temp.summary);
    perm.sort_str = strdup(temp.sort_str);
    return perm;
}

Answer 1

Most likely, your problem is not mktime, but one of your copy statements. First one is

strncat(time_str, temp.stime, 6);

with this time_str is likely not NUL terminated.

Same here

strncpy(temp.end, buffer, 8);
strncpy(temp.start, buffer, 8);

temp.end and temp.start might be NUL terminated, when they were before, but you can't be sure. Just use strcpy instead.

Next one is

calendar[percent_full] = cpystruct(temp, is_location);
printst(calendar[percent_full]);
percent_full++;

I see no check for the end of calendar. So there might be a write beyond the end of calendar.

As an aside, when you do

if(caltime.tm_isdst == 1){
    caltime.tm_hour -= 1;
}

tm_hour might become negative.