Question

I need help fixing this code in C. It keeps giving me an error saying error: ‘O_RDWD’ undeclared (first use in this function) if ((fd = open(fifo, O_RDWD)) < 0)

note: each undeclared identifier is reported only once for each function it appears in. Please fix so it compiles properly.

//**************************************************************************************************************************************************

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

#define MSGSIZE 63

char *fifo = "fifo";

int main(int argc, char **argv){
   int fd;
   char msgbuf[MSGSIZE + 1];

   if (mkfifo(fifo, 0666) == -1 ){
       if (errno != EEXIST) {
           perror("receiver: mkfifo");
           exit(4);
       }
   }

   if ((fd = open(fifo, O_RDWD)) < 0) {   //note O_RDWD, change it to O_RD?
       perror("fifo open failed");
       exit(5);
   }

   for (;;){

       int num=read(fd, msgbuf, MSGSIZE + 1);
       if (num < 0) {
               perror("message read failed");
               exit(6);
       }
       //including the following when O_RDONLY
       /*
       if (num == 0) {
               printf("nothing to read or no write end.\n");
               continue;
       } */  
       printf("message received:%s\n", msgbuf);
   }
}

Answer 1

use O_RDWR instead of O_RDWD.

O_RDWR is used to open file.

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

#define MSGSIZE 63

char *fifo = "fifo";

int main(int argc, char **argv){
   int fd;
   char msgbuf[MSGSIZE + 1];

   if (mkfifo(fifo, 0666) == -1 ){
       if (errno != EEXIST) {
           perror("receiver: mkfifo");
           exit(4);
       }
   }

   if ((fd = open(fifo, O_RDWR)) < 0) {   //note O_RDWD, change it to O_RD?
       perror("fifo open failed");
       exit(5);
   }

for (;;){

       int num=read(fd, msgbuf, MSGSIZE + 1);
       if (num < 0) {
               perror("message read failed");
               exit(6);
       }
       //including the following when O_RDONLY
       /*
       if (num == 0) {
               printf("nothing to read or no write end.\n");
               continue;
       } */  
       printf("message received:%s\n", msgbuf);
   }
}