Programming with FIFO: mkfifo(), mknod()

FIFOs can be created from the shell. But they can also be created using programs. There are two ways by which FIFOs can be created from the program

Creating a FIFO

1. mknod

Syntax

int mknod(const char *pathname, mode_t mode, dev_t dev);

where pathname corresponds to the fifo name, mode corresponds to the file permissions. Since mknod can be used to create a regular file, block or charcter special files and fifo. We have to specify the file type. Corresponding to FIFO: the file type is S_IFIFO.

#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>

int main(int argc, char *argv[]){
     int result;
     if (argc != 2) {
             fprintf(stderr, "Usage: ./a.out fifoname\n");
             exit (1);
     }

     result = mknod (argv[1], S_IRUSR| S_IWUSR|S_IFIFO, 0);
     if (result < 0) {
          perror ("mknod");
          exit (2);
       }
  }

Here we wish to give both read and write permissions to the user. So we specified S_IRUSR | S_IWUSR| S_IFIFO in the mode. If the file type is S_IFCHR or S_IFBLK then dev is checked; otherwise it is ignored. So we passed 0 as the argument.

2. mkfifo

Syntax

int mkfifo(const char *pathname, mode_t mode);

where pathname correspnds to fifo name and mode corresponds to file mode.

 # include <stdio.h>
 # include <stdlib.h>
 # include <sys/types.h>
 # include <sys/stat.h>

int main(int argc, char *argv[]){
     int result;

     if (argc != 2) {
          fprintf(stderr, "Usage: ./a.out fifoname\n");
          exit (1);
     }

    result = mkfifo (argv[1], S_IRUSR| S_IWUSR);
     if (result < 0) {
          perror ("mkfifo");
          exit (2);
      }
  }

Here we need not explicitly specify the file type S_IFIFO. You can (if you wish) specify S_IFIFO in the mode.