[erlang-questions] "Port reading stdout from external program"

[Frank Muller]

Use erlexec in "async" mode instead:
https://github.com/saleyn/erlexec


Le mer. 16 nov. 2016 à 20:43, Stanislaw Klekot <erlang.org@REDACTED> a
écrit :

> On Wed, Nov 16, 2016 at 08:06:03PM +0100, Alex Feng wrote:
> > Hi,
> >
> > I am using an port to communicate with an external program, I would like
> to
> > fetch each output from the external problem.
> > But I have problem to fetch the output when the external problem runs
> into
> > waiting input," scanf " for example.
> >
> > Here is an example to communicate with a simple C program.
> >
> > I need to fetch the prompt line("Please input you name") from Port in
> order
> > to interact with C code,  but with "scanf" added in C code, I couldn't
> > fetch it from Port.
> > Does anyone know why is that ?  Any advice and suggestions will be
> greatly
> > appreciated.
> [...]
> > C code:
> >
> > int main()
> > {
> >
> >   char str[10];
> >
> >   printf("Please input you name:");  //Prompt line
> >
> >   scanf ("%9s",str);  // with this line, port can not read the output
> from this program.
> >
> >   return 1;
> > }
>
> It's because STDOUT buffering differs between running things in terminal
> directly and running them with STDOUT redirected somewhere. You can see
> it yourself by first running this "a.out" in shell, and then running it
> redirected to cat: "a.out | cat". In the latter case you won't get
> prompt.
>
> You need to call fflush() to flush anything buffered by printf() (see
> its man page for details).
>
> --
> Stanislaw Klekot
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