Subj : Re: named pipe problem on linux
To   : comp.lang.c++,comp.os.linux
From : Larry I Smith
Date : Mon Nov 01 2004 07:15 pm

richard wrote:
> I have a simple test to pass information from a client to a server 
> using named pipe. what I really want is: when I type a line on the client,
> the server will output the line immediately. but to my surprise, I always 
> have to terminate the client to get the server in action, i.e. prints out
> what I typed.
> 
> anything I missed? I am compiling using gcc without any option.
> 
> thanks,
> ---RICH
> 
> ---------------------
> server
> ---------------------
> #include <stdio.h>
> #include <stdlib.h>
> #include <sys/stat.h>
> #include <unistd.h>
>  
> #include <linux/stat.h>
>  
> #define FIFO_FILE       "MYFIFO"
>  
> int main(void)
> {
>         FILE *fp;
>         char readbuf[80];
>  
>         /* Create the FIFO if it does not exist */
>         umask(0);
>         mknod(FIFO_FILE, S_IFIFO|0666, 0);
>  
>         while(1)
>         {
>                 fp = fopen(FIFO_FILE, "r");
>                 fgets(readbuf, 10, fp);
>                 printf("Received string: %s\n", readbuf);
>                 fclose(fp);
>         }
>  
>         return(0);
> }
> 
> -------
> client
> -------
> #include <stdio.h>
> #include <stdlib.h>
>  
> #define FIFO_FILE       "MYFIFO"
>  
> int main(int argc, char *argv[])
> {
>         FILE *fp;
>  
>                 char str[20];
>  
>         if((fp = fopen(FIFO_FILE, "w")) == NULL) {
>                 perror("fopen");
>                 exit(1);
>         }
>  
>                 while( scanf("%s", str) != EOF  )
>                 {                       fputs(str, fp);
>                                         fputs(str, stdout);
>                 }
>  
>         fclose(fp);
>         return(0);
> }
> 

<---- updated server: ---->

// named pipe server

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

#include <linux/stat.h>

#define FIFO_FILE       "MYFIFO"

int main(void)
{
     FILE *fp;
     char readbuf[80];

     fprintf(stderr, "Pipe server running...\n");

     // try to open my fifo file.  it may already exist from
     // an earlier aborted execution
     fp = fopen(FIFO_FILE, "r");

     // if the fopen failed, the fifo file does not exist
     if (NULL == fp)
     {
         // Create the FIFO file
         umask(0);
         if(mknod(FIFO_FILE, S_IFIFO|0666, 0))
         {
            fprintf(stderr, "mknod() failed\n");
            return 1;
         }

         fp = fopen(FIFO_FILE, "r");  // now open the fifo file
     }

     printf("Receiving...\n");

     // while we can read (up to 9) chars from the fifo...
     // Note: readbuf[] will be nul-terminated and will
     // include any newlines read from the pipe.  since
     // we are reading so few bytes at once (9) it will
     // take several iterations of the 'while loop' to read
     // any long lines written to the pipe by clients.
     while(NULL != fgets(readbuf, 10, fp))
     {
         // print the string just read to my stdout
         printf("%s", readbuf);
         fflush(stdout);
     }

     fclose(fp);  // close the fifo file

     remove(FIFO_FILE);  // delete the fifo file

     fprintf(stderr, "Pipe server terminating.\n");

     return(0);
}


<---- updated client: ---->

// named pipe client

#include <stdio.h>
#include <stdlib.h>

#define FIFO_FILE       "MYFIFO"

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

     char str[20];

     // try to open an existing fifo file
     if((fp = fopen(FIFO_FILE, "w")) == NULL)
     {
         perror("fopen");
         exit(1);
     }

     // get up to 19 chars from stdin into str[].
     // str[] will be nul-terminated and any newlines in
     // the input will be written to the pipe (fp).
     while( fgets(str, sizeof(str), stdin) != NULL  )
     {
         // write the chars read from stdin to the pipe
         fprintf(fp, "%s", str);
         fflush(fp);  // flush any buffered IO to the pipe

         // echo what I wrote to the pipe to my stdout
         fprintf(stdout, "Sent: %s\n", str);
         fflush(stdout);
     }

     fclose(fp);  // close the pipe

     return(0);
}

Regards,
Larry

-- 
Anti-spam address, change each 'X' to '.' to reply directly.

.