Question

I am trying to make this work but no luck, basically i need to write to the pipe and then make the pipe return back with the text i sent. I have a server.c and client.c , so i make the server.c run…, open a new terminal and then run the client.. the problem is that the client doesnt do anything when i run it.. I am sure i am missing something.. like closing the pipe. i am not sure.. I would really appreciate some guidance

server.c

#include <stdio.h>
#include <errno.h>
#include <ctype.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <string.h>
#define PIPE1      "PIPE1"
#define PIPE5      "PIPE5"

#define MAX_BUF_SIZE    255

int main(int argc, char *argv[])
{
    int rdfd1,rdfd2,rdfd3,rdfd4, wrfd1,wrfd2,wrfd3,wrfd4,ret_val, count, numread1,numread2,numread3,numread4;
    char buf1[MAX_BUF_SIZE];
    char buf2[MAX_BUF_SIZE];
    char buf3[MAX_BUF_SIZE];
    char buf4[MAX_BUF_SIZE];

    /* Create the first named - pipe */
    ret_val = mkfifo(PIPE1, 0666);


    if ((ret_val == -1) && (errno != EEXIST)) {
        perror("Error creating the named pipe");
          return 1; 
    }



    ret_val = mkfifo(PIPE5, 0666);

    if ((ret_val == -1) && (errno != EEXIST)) {
        perror("Error creating the named pipe");
        return 1; 
    }

    /* Open the first named pipe for reading */
    rdfd1 = open(PIPE1, O_RDONLY);


    /* Open the first named pipe for writing */
    wrfd1 = open(PIPE5, O_WRONLY);


    /* Read from the pipes */
    numread1 = read(rdfd1, buf1, MAX_BUF_SIZE);


    buf1[numread1] = '0';

    printf("Server : Read From the  pipe : %sn", buf1);


    /* 
     * Write the converted content to 
     * pipe 
     */    
   write(wrfd1, buf1, strlen(buf1));

}

client.c

#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <ctype.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#define PIPE1      "PIPE1"
#define PIPE5      "PIPE5"


#define MAX_BUF_SIZE    255


int main(int argc,  char *argv[ ]) {
   pid_t childpid;             
   int error;                  
   int i;                     
   int nprocs;                
           /* check command line for a valid number of processes to generate */

   int wrfd1, rdfd1, numread;
    char rdbuf[MAX_BUF_SIZE];

   if ( (argc != 2) || ((nprocs = atoi (argv[1])) <= 0) ) {
       fprintf (stderr, "Usage: %s nprocs\n", argv[0]);
       return 1; 
   }  



   for (i = 1; i < nprocs;  i++) {  
       /* create the remaining processes */

            if ((childpid = fork()) == -1) {
                  fprintf(stderr, "[%ld]:failed to create child %d: %s\n", (long)getpid(), i, strerror(errno));
                   return 1; 
                } 

          /* Open the first named pipe for writing */
          wrfd1 = open(PIPE5, O_WRONLY);

          /* Open the second named pipe for reading */
         rdfd1 = open(PIPE1, O_RDONLY);


         if (childpid)
         break;

           char string1[100];

            if(sprintf(string1, "This is process %d with ID %ld and parent id %ld\n", i,  (long)getpid(), (long)getppid())) {
              write(wrfd1,string1, strlen(string1));
              }

         /* Read from the pipe */
         numread = read(rdfd1, rdbuf, MAX_BUF_SIZE);

         rdbuf[numread] = '0';

         printf("Full Duplex Client : Read From the Pipe : %sn", rdbuf);    
      } 


   return 0; 
}  

Answer 1

It seems like both server and client read from PIPE1 and write to PIPE5. Shouldn’t one of them write to PIPE1 so that the other can read it from the other end?

Also, if you’re testing with ./client 1, your for (i = 1; i < nprocs; i++) loop will never execute.

One last thing, see this question. I’m not entirely sure it applies to your code, but it’s worth keeping in mind.