pipe.c

/* basic pipelining, 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/types.h> // for shmdet
 # include <string.h> // for strcpy

 # define SIZE 1024 // message size
 # define exception(x) { puts(x); exit(1); }

 int main(int argc, char * argv[])
    {
     /* creating a FIFO queue */
     char msg[SIZE];
     int pid, isparent, fd[2], val; // *fd is for reading, *++fd is for writing
     val = pipe(fd); // creates the pipe
     // if(val == -1) exception("Pipe creation failed");
     pid = fork(); // generates child process
     // if(pid == -1) exception("Fork error");
     /* child process: reader */
     if(pid == 0)
    {
     close(fd[1]); // always close the buffer before starting to read!
     while(read(fd[0], msg, SIZE) > 0) // reads all messages
        printf(msg);
     close(fd[0]); // closes the other buffer
    }
     /* parent process: writer */
     else
    {
     close(fd[0]); // same consideration applies
     puts("Input text to transfer (or 'quit'): ");
     do {
         fgets(msg, SIZE, stdin); // reads message from standard input (keyboard)
         write(fd[1], msg, SIZE); // writes message
         printf("Message: %s", msg); // prints message
     } while(strcmp(msg, "quit\n") != 0);
     close(fd[1]);
     wait(&isparent); // waits for child death (end of reading)
    }
     /* see pg. 50 for analogous example with mkfifo() */
     return 0;
    }