Subj : Re: named pipe problem on linux
To   : comp.lang.c++,comp.os.linux
From : richard
Date : Tue Nov 02 2004 04:02 pm

On Mon, 01 Nov 2004 19:15:35 +0000, Larry I Smith wrote:

> 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


thanks, Larry.

.