Trouble with named pipe...

Good evening,

I am trying to use a named pipe to implement communication between two UNIX commands. It does not compile properly. The error message in Dev-C++ is "syntax error before numeric constant". What am I missing?

Code:

---

 

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

int main(int argc, char *argv[]){
pid_t pid;
int fd[2];
int val;

int mkfifo(const char *myFifo, 0644);            /* create a named pipe */                               

pid = fork();                                        /* fork */
        if(pid < 0){
                printf("Cannot fork");
                exit(1);
        }
        if(pid > 0){
                /* parent process */
                dup2(fd[1], 1);                       
                close(fd[0]);                       
                execlp("ps", "ps", "-ef", (char *)0);
        }
        else if(pid == 0){
                /* child process */
                dup2(fd[0], 0);                       
                close(fd[1]);                       
                execlp("grep", "grep", "ct321j", (char *)0);
        }

}

---

Thanks!

Damien

Code:

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int mkfifo(const char *myFifo, 0644);            /* create a named pipe */

---

Did you intend this to be a function call? If so, don't use function prototype syntax for it, but make it look like every other function call in your program.

Troubles continue...It does not appear as if the pipe is working. The first part, "ps -ef" is working but not the second part.

Ideas as to why?

Code:

---


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

int main(int argc, char *argv[]){
pid_t pid;
int fd[2];
int pipe;

mkfifo("/p2/myFIFO", O_WRONLY);  /* create a named pipe */
   
pid = fork();          /* fork */
 if(pid < 0){
  printf("Cannot fork");
  exit(1);
 }
 if(pid > 0){
  /* parent process */
        dup2(fd[1], 1); 
  close(fd[0]); 
  execlp("ps", "ps", "-ef", (char *)0);
 }
 else if(pid == 0){
  /* child process */
  dup2(fd[0], 0); 
  close(fd[1]); 
  execlp("grep", "grep", "cm415b", (char *)0);
 }
}

---

You would have to define "second part" and "not working" for us to get anywhere.

Evening!

What I mean is that the parent process executes "ps -ef" and sends it down the pipe to the child process which uses it as input for grep. I have an example of the unnamed pipe which works as it should. When I run the named pipe, it appears to only run "ps -ef".

Code:

---


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

int main(int argc, char *argv[]){
pid_t pid;
int fd[2];
int pipe;

mkfifo("/p2/myFIFO", O_WRONLY);  /* create a named pipe */
   
pid = fork();          /* fork */
 if(pid < 0){
  printf("Cannot fork");
  exit(1);
 }
 if(pid > 0){
  /* parent process */
        dup2(fd[1], 1); 
  close(fd[0]); 
  execlp("ps", "ps", "-ef", (char *)0);
 }
 else if(pid == 0){
  /* child process */
  dup2(fd[0], 0); 
  close(fd[1]); 
  execlp("grep", "grep", "cm415b", (char *)0);
 }
}

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Are you expecting fd[1] to be your named pipe? If so, wouldn't you need to put that in your dup2 call instead of stdout?