While doing 80 mph down the road on my motorcycle it suddenly dawned on
me why the pipe was echoing.... I think of the damnest things at the
damnest times :-).....
On the same pipe set 0 is hooked to 1, Duh..... Another head up butt.
You have to create TWO pipes, one for output and one for input. closing
the ones not needed.
That fixed the echo problem... But, not the child's printf()/puts() not
making it through the pipe... The parents either for that matter.....
You stiil have to use read()/write() calls. Is not a printf("%s", line)
or puts(line) use the same file as write(STDOUT_FILENO, line,
strlen(line)??? The child's STDIN_FILENO and STDOUT_FILENO have been
closed/dup'ed with the in/out pipes.
Jeff PIerce wrote:
>
> # To subscribers of the xforms list from Jeff PIerce <piercej@preferred.com> :
>
> This isn't really a xforms questions,but it occured during xforms app
> development...
>
> I am working on a xforms mp3 player... I am using mpg123 as the actual
> player, forking it from the app. No problem....
>
> There is a version of mpg123 for interactive use called mpg123m. It is
> included with the tk3play app. mpg123m not only accepts futher commands
> while it is playing, it also gives progress, play time, blocks played,
> etc, will it is running.
>
> tk3play uses it's pipes to send and get data. No problem I thought. Just
> use pipes in C.
>
> Big problems, at least to me....
>
> Pipes don't work like I thought.....
>
> I set up a command line test app to spawn mpg123 and take further
> commands from inut lines and send it to the mpg123m child . No problem.
> I start my app which spawns mpg123m. I then enter 2 0mp3/cobramp3 ( the
> command mpg123 expects to begin playing a file) which is read by my app
> and sent through outPipe[1] to mpg123m. It starts playing and it's
> progress output comes to the screen.
>
> I then add the pipe for the output of the child (mpg123m) to come back
> to the parent...NO GO......
>
> I try a test app and child to get better aquainted with pipes...
>
> I find that if the child wants to send back it HAS to use a write() and
> not puts() or printf().
>
> I find that if the parent writes out pipe[0], it is echoed back to
> pipe[1].
>
> How do you overcome these problems.
>
> How do you turn off the echo between pipes[0] and pipes[1] at the
> parent????
>
> Why is the child not piping back to the parent when it uses puts() or
> printf()??? This means that you cannot get the output of an app piped
> back unless that app dows not use puts()'s and printf()'s.... How can
> tht be quarantied????
>
> I understand that printf() uses streams (FILE *) while write() uses file
> descriptors(integers). But, I thought that printfputs mapped to
> STDOUT_FILENO....
>
> --
> Jeff Pierce
> piercej@preferred.com
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-- Jeff Pierce piercej@preferred.com _________________________________________________ To unsubscribe, send the message "unsubscribe" to xforms-request@bob.usuhs.mil or see http://bob.usuhs.mil/mailserv/xforms.html XForms Home Page: http://bragg.phys.uwm.edu/xforms List Archive: http://bob.usuhs.mil/mailserv/list-archives/