signals.c

 /* basic signals, UNIX-native */

 /* pointer arithmetics:
  *
  * push(pointer, v) INDICATES *(pointer++) = v
  * pop(pointer) INDICATES *(--pointer)
  * (*++v)[0] INDICATES (**++v)
  *           INDICATES first char in v
  *           INDICATES name of string/vector v
  * likewise, *v[0] INDICATES **v
  *       and *v[n] INDICATES **(v + n)
  * returntype (*funct)(args) INDICATES a function funct with arguments args which returns...
  * char **argv INDICATES pointer to char pointer
  * int(*v)[len] INDICATES pointer "v" to a vector of "len" int elements
  * int *v[len] INDICATES vector "v" of "len" pointers to int elements
  * void *funct() INDICATES function "funct" that returns a pointer-to-void
  * void (*funct)() INDICATES pointer to a function "funct" that returns void
  *
  */

 /* useful characters: [] # */

 # include <stdio.h>
 # include <stdlib.h> // for exit
 # include <signal.h>
 # include <sys/shm.h> // for shmdet
 # include <sys/sem.h>
 # include <fcntl.h> // for O_RDWR

 # define BUFFER 256
 # define exception(x) { puts(x); exit(1); }

 void timeout();
 char c; // input char

 int main(int argc, char * argv[])
    {
     /* ALARM example; NOTE: DOES NOT STOP */
     alarm(2); // 2t left before alarm
     signal(SIGALRM, timeout);
     printf("Alarm signal sent\n");
     // while(1) read(0, &c, 1); // reads chars from input

     /* KILL example */
     int pid; // ID of the process to be killed
     printf("Enter server PID: ");
     scanf("%d", &pid);
     kill(pid, SIGTERM);
    }

  /* waits on timeout, then signals */
  void timeout()
    {
     printf("Wake up call\n");
     signal(SIGALRM, timeout); // sends timeout; NOTE: the wakeup executes at regular intervals until the PID is entered, possibly due to recursion?
     alarm(2);
    }

 /* samples at pgs. 63-64 with server-client model */