fifo.c

 /* basic FIFO operations, 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 <sys/ipc.h>
 # include <sys/shm.h> // for shmdet
 # include <sys/stat.h> // for message flags (O_*)
 # include <sys/types.h> // for shmdet
 # include <fcntl.h> // for O_RDWR
 # include <string.h> // for strcpy

 # define RSIZE 20 // reply size
 # define exception(x) { puts(x); exit(1); }

 typedef struct {
   long type;
   char reply[RSIZE];
 } request;

 int main(int argc, char * argv[])
    {
     /* using a FIFO */
     int pid, fifo, file, success;
     request req;
     char replymsg[RSIZE];
     printf("Type lowercase char: "); scanf("%s", req.reply); // scans the input and saves it
     // if(req.reply[0] > 'z' || req.reply[0] < 'a') exception("Invalid input char");
     req.reply[1] = '\0'; // now the char is a string
     success = mkfifo(req.reply, IPC_CREAT|0666);
     // if(success == -1) exception("Error in FIFO creation");
     file = open("secondalias.txt", 1);
     // if(file == -1) exception("Error in file opening");
     success = write(file, &req, sizeof(request)); // writes data
     success = close(file);
     file = open(req.reply, O_RDWR); // transfers the reply on the file
     success = read(file, replymsg, RSIZE); // reads the file
     printf("Reply: '%s'\n", replymsg); // prints it
     success = close(file);
     success = unlink(req.reply);

     return 0;
    }