Re: Help on pipe

["Michał Nazarewicz" <m.nazarewicz@samsung.com>]

On Fri, 10 Jul 2009 08:22:54 +0200, Ardhan Madras <nightdecoder@gmail.com>  
wrote:

> #include <sys/types.h>
> #include <sys/wait.h>
> #include <unistd.h>
> #include <stdio.h>
> #include <string.h>
>
> int main(void)
> {
>   pid_t pid;
>   int fds[2], ret;
>   const char *sort = "/usr/bin/sort";

"static const char sort[]" would be better IMO.

>   char *argv[2] = { "sort", NULL };

"static const char *argv[]" is definitly better here and does not produce  
warnings.  Your code discards "const" from pointer (a string literal).

>   ret = pipe(fds);
>   if (ret == -1) {
>     perror("pipe");
>     return -1;
>   }
>   pid = fork();
>   if (pid == -1) {
>     perror("fork");
>     return -1;
>   }

Personally I preffer something like:

   switch (fork()) {
   case -1: /* error */  break;
   case  0: /* child */  break;
   default: /* parent */
   }

but suit yourself.

>   if (pid == 0) {
>     int ret;

No need to define this variable here.  You already have such variable.

>
>     close(fds[1]);
>     dup2(fds[0], STDIN_FILENO);
>
>     ret = execve(sort, argv, NULL);
>     if (ret == -1) {
>       perror("execve");
>     }
>     close(fds[0]);
>     _exit(0);

No need to close(), and _exit(0) should be _exit(1) (or -1 if you will)  
since the chiled finished with error.

>   }
>   else {
>     FILE *stream;
>
>     close(fds[0]);
>     stream = fdopen(fds[1], "w");
>     if (!stream) {
>       perror("fdopen");
>       return -1;
>     }
>     fprintf(stream, "this\n");
>     fprintf(stream, "means\n");
>     fprintf(stream, "war\n");
>     fflush(stream);

And here, replace fflush() with fclose().  It seems, data is buffered on  
kernel level, not only libc level and fflush() cannot handle that.

>     waitpid(pid, &ret, 0);
>     close(fds[1]);

No need to close.

>   }
>   return 0;
> }

-- 
Best regards,                                            _     _
  .o. | Liege of Serenly Enlightened Majesty of         o' \,=./ `o
  ..o | Computer Science,  Michał "mina86" Nazarewicz      (o o)
  ooo +-<m.nazarewicz@samsung.com>-<mina86@jabber.org>-ooO--(_)--Ooo--

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