added a write function, and a questionable read function

main.c

@@ -2,6 +2,14 @@
 #include <stdlib.h>
 #include <time.h>
 #include <signal.h>
+#include <string.h>
+
+#define DATFILE "/home/randomuser/datfile"
+
+time_t buf;
+struct tm bt;
+struct tm et;
+int flg = 0;
 
 struct time {
     int hour;
@@ -14,42 +22,88 @@ struct date {
 };
 struct session {
     struct date date;
-    struct time time;
-    int minutes;
-    char *name;
+    int offset;
+    char name[4096];
 };
 
-time_t buf;
-struct time buf2;
-struct tm bt;
-struct tm et;
-int flg = 1;
+void sighnd() { flg = 1; }
+void flgwt() { while(flg == 0) { continue; } }
 
+char* concat(const char *s1, const char *s2) {
+    char *result = malloc(strlen(s1) + strlen(s2) + 1);
+    // let's hope malloc works correctly
+    strcpy(result, s1);
+    strcat(result, s2);
+    return result;
+}
 
-void sighnd() { flg = 0; }
-void flgwt() { while(flg) { continue; } }
+struct tm getTime() {
+    time_t buf;
+    struct tm b;
+    buf = time(NULL);
+    b = *localtime(&buf);
+    return b;
+} 
 
-int writeData(int fd, struct session session);
+void writeSession(FILE *fd, struct session session) {
+    fprintf(fd, "P%02d%02d%04d%d %s\n",
+        session.date.month, session.date.day, session.date.year,
+        session.offset, session.name);
+}
 
-struct time timediff(struct tm f, struct tm l) {
-    struct time tmp;
-    tmp.hour = f.tm_hour - l.tm_hour;
-    tmp.min = f.tm_min - l.tm_min;
-    return tmp;
+struct session dataToSession(struct tm time, int offset, char *name) {
+    struct session session;
+    session.date.year = time.tm_year + 1900;
+    session.date.month = time.tm_mon;
+    session.date.day = time.tm_mday;
+    session.offset = offset;
+    strcpy(session.name, name);
+    return session;
+}
+
+struct session lineToSession(char *line) {
+    struct session session;
+    char *buf = line;
+    char *parameters = strtok(buf, " ");
+    strcpy(session.name, strtok(NULL, ""));
+    session.date.month = atoi(concat(&parameters[1], &parameters[2]));
+    session.date.day = atoi(concat(&parameters[3], &parameters[4]));
+    session.date.year = atoi(concat(
+        concat(&parameters[5], &parameters[6]),
+        concat(&parameters[7], &parameters[8])));
+    char charbuf[8];
+    for(int i = 9; parameters[i] == " "; i++) {
+        strcat(&charbuf, &parameters[i]);
+    }
+    session.offset = atoi(&charbuf);
+    return session;
+}
+
+int timediff(struct tm f, struct tm l) {
+    int fm = f.tm_min + (f.tm_hour * 60);
+    int lm = l.tm_min + (l.tm_hour * 60);
+    return fm - lm;
 }
 
 int main(int argc, char **argv) {
-    buf = time(NULL);
-    bt = *localtime(&buf);
-    printf("%d:%02d:%02d\n", bt.tm_hour, bt.tm_min, bt.tm_year + 1900);
+    if (argc != 2) { 
+        FILE *f = fopen(DATFILE, "a");
+        char *line;
+        struct session buffer;
 
+        while(fgets(line, sizeof(line), f)) {
+             buffer = lineToSession(&line);
+             writeSession(f, buffer);
+        }
+        return 1;
+    }
+    bt = getTime();
     signal(SIGINT, sighnd);
     flgwt();
-    buf = time(NULL);
-    et = *localtime(&buf);
-    printf("%d:%02d:%02d:%02d\n", et.tm_hour, et.tm_min, et.tm_sec, et.tm_year + 1900);
-    buf2 = timediff(et, bt);
-    printf("%i:%i difference\n", buf2.hour, buf2.min);
-    printf("exiting lol\n");
+    int t = timediff(getTime(), bt);
+    struct session data = dataToSession(bt, t, argv[1]);
+    FILE *f = fopen(DATFILE, "a");
+    writeSession(f, data);
+    fclose(f);
     return 0;
 }