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From: edw@ius2.cs.cmu.edu (Eddie Wyatt)
Newsgroups: comp.unix.wizards
Subject: Re: reading from terminal
Message-ID: <1189@ius2.cs.cmu.edu>
Date: Mon, 8-Jun-87 23:21:11 EDT
Article-I.D.: ius2.1189
Posted: Mon Jun  8 23:21:11 1987
Date-Received: Sat, 20-Jun-87 09:00:14 EDT
References: <7749@brl-adm.ARPA>
Organization: Carnegie-Mellon University, CS/RI
Lines: 71

In article <7749@brl-adm.ARPA>, jfjr@mitre-bedford.arpa (Freedman) writes:
> 
>   This may be a trivial question to the wizards but  I am a unix
> novice (~3 months).  I need to read a character from the terminal
> without stopping a program.  I have a program thats going to
> do a lot of interesting things you wouldn't be interested in.
> I want to give the user the ability to halt the processing
> at any time - poke around the program and then resume processing.
> While the program is doing its thing all sorts of terminal and
> file i/o are happening. I have done this successfully and simply
> on VMS using qio with the proper flag but I am having problems
> doing it on Unix. I would rather not have to do this trick by
> using a second process nor would I want to usurp Control-C.
> 
>   I really must say that Unix documentation compared to
> VMS doesn't measure up( or maybe I am looking in the wrong
> places if so enlighten me) 
> 
>                                    Thirster after knowledge
> 
> Jerry Freedman, Jr       "If at first you don't succeed, lower your standards"
> jfjr@mitre-bedford.arpa
> (617)271-6248 or 8658    


    The functions you want to look into are ioctl (i/o control) or
stty (set tty). Do a "man 4 tty" to find what all the options to ioctl are.


   To do what you want to do :


enable_quick_input()
    {
    struct sgttyb mode;
    int fd = fileno(stdin);

    gtty(fd, &mode);            /* get old mode */
    mode.sg_flags &= ~RAW;      /* process special characters like ^H */
    mode.sg_flags &= ECHO;	/* make sure echo is on */
    mode.sg_flags &= CBREAK;    /* make characters available to process
				   as soon as they are typed (this may
				   disable cooked mode). */
    stty(fd, &mode);		/* set mode */
    }

 I  believe that will do it.

  To poll for input you can use select if you want. But that's a little slow
so use ioctl().



int ready_to_read(fd)
    int fd; /* a file desciptor, not a FILE pointer here */
    {
    int num;

    ioctl(fd,FIONREAD,(char *)&num);
    return(num > 0);
    }


Which brings up a question.  Does anyone know of a quicker way of determining
if any characters are on a port other than using ioctl (select is slower, at
least by what I have measured)?

-- 
					Eddie Wyatt

e-mail: edw@ius2.cs.cmu.edu