Two i/o questions

**Jerry Coffin** · Jun 27 '08, 04:47 PM

Re: Two i/o questions

In article <685c8634-bcfd-4f7e-b869-0d0e5c01dc20
@m73g2000hsh.go oglegroups.com> , isliguezze@gmai l.com says...

How do I do in C++ (!) this operation (usin C99 stdlib.h):
>
fflush(stdin);

This gives undefined behavior in C. There are many ways to get undefined
behavior in C++, though I'm not sure why you'd want to do so.

And how do I make something like "Press any key to continue..." in
standard way? I mean if I use getchar() (again from C99), if requires
pressing <Enterkey. How do I do it without pressing <Enter>? Any
unbuffered standard C++ variant? Maybe some std::cin member function?

No. C++ allows you to _view_ the I/O in different ways, but the basic
requirements it makes of the underlying system are essentially identical
to those of C.

--
Later,
Jerry.

The universe is a figment of its own imagination.

**Daniel Pitts** · Jun 27 '08, 04:47 PM

Re: Two i/o questions

Isliguezze wrote:

How do I do in C++ (!) this operation (usin C99 stdlib.h):
>
fflush(stdin);

What does flusing stdin give you? flushing will cause buffered data to
be pushed out.

>
And how do I make something like "Press any key to continue..." in
standard way? I mean if I use getchar() (again from C99), if requires
pressing <Enterkey. How do I do it without pressing <Enter>? Any
unbuffered standard C++ variant? Maybe some std::cin member function?

It is implementation specific. I remember in Borland C++ 3.1, there was
a getch() function that did what you want. Its better to just say "Press
enter to continue..." and leave it at that if you want portability.

--
Daniel Pitts' Tech Blog: <http://virtualinfinity .net/wordpress/>

**osmium** · Jun 27 '08, 04:47 PM

Re: Two i/o questions

"Isliguezze " wrote:

How do I do in C++ (!) this operation (usin C99 stdlib.h):
>
fflush(stdin);

To clear the input buffer maintained by the system, see istream::ignore ().
You may have to precede it with ios::clear() because the stream is in a fail
state and it will not listen to any command but clear. There are ways to see
if the stream is in a fail state.

And how do I make something like "Press any key to continue..." in
standard way? I mean if I use getchar() (again from C99), if requires
pressing <Enterkey. How do I do it without pressing <Enter>? Any
unbuffered standard C++ variant? Maybe some std::cin member function?

The only ways I know of doing "Press any key" are non-standard. Only
Microsoft would think that the up arrow key and it's cousins was not a key,
so the message was wrong from the get-go. Easiest way out is to use "Press
enter" and get rid of any undesired input.

**Isliguezze** · Jun 27 '08, 04:47 PM

Re: Two i/o questions

You see, I need to fflush() because I want to "Press any key to
continue..." If there's something inside the buffer, that function
used to halt the screen reads that and screen dies quickly... Of
course, in Win/DOS I can use system("PAUSE") ;, In good old :) Borland
3.1 getch() or getche(), is there a portable(standa rd) C++ function to
do that?

**Default User** · Jun 27 '08, 04:47 PM

Re: Two i/o questions

Isliguezze wrote:

You see, I need to fflush() because I want to "Press any key to
continue..." If there's something inside the buffer, that function
used to halt the screen reads that and screen dies quickly...

You can't get fflush() to do that portably. It doesn't really matter,
because you can't get the other thing either. You need to find a
platform-specific group for your questions.

Brian

**James Kanze** · Jun 27 '08, 04:47 PM

Re: Two i/o questions

On Jun 25, 10:45 pm, "Default User" <defaultuse...@ yahoo.comwrote:

Isliguezze wrote:

You see, I need to fflush() because I want to "Press any key
to continue..." If there's something inside the buffer, that
function used to halt the screen reads that and screen dies
quickly...

You can't get fflush() to do that portably. It doesn't really
matter, because you can't get the other thing either. You need
to find a platform-specific group for your questions.

Yes and no. Curses (or ncurses) is a pretty portable library,
available for many platforms; if you're trying to do anything
fancy in a classical "tty" window (console window under Windows,
xterm or whatever under Unix, etc.), then it's surely the way to
go.

Of course, if all you really want is to block output until the
user has acknowledged reading it: "Press enter to continue..."
and std::getline() are the simplest solutions.

--
James Kanze (GABI Software) email:james.kan ze@gmail.com
Conseils en informatique orientée objet/
Beratung in objektorientier ter Datenverarbeitu ng
9 place Sémard, 78210 St.-Cyr-l'École, France, +33 (0)1 30 23 00 34

**James Kanze** · Jun 27 '08, 04:47 PM

Re: Two i/o questions

On Jun 25, 6:37 pm, "osmium" <r124c4u...@com cast.netwrote:

"Isliguezze " wrote:

[...]

The only ways I know of doing "Press any key" are
non-standard. Only Microsoft would think that the up arrow
key and it's cousins was not a key, so the message was wrong
from the get-go.

I don't know about the up arrow key, but I've yet to see a
program which responded to the control key or the shift key in
such cases.

(Back in the old days, before anyone had even heard of the term
"computer literacy", you'd occasionally see such messages in
demo programs at technical fairs. At which point, I'd call one
of the sales droids over, and point out that the program wasn't
working by hitting the control key. Nine times out of ten, the
sales droid would then go off to find some technical support
person to fix it.)

--
James Kanze (GABI Software) email:james.kan ze@gmail.com
Conseils en informatique orientée objet/
Beratung in objektorientier ter Datenverarbeitu ng
9 place Sémard, 78210 St.-Cyr-l'École, France, +33 (0)1 30 23 00 34

**Daniel Pitts** · Jun 27 '08, 04:47 PM

Re: Two i/o questions

James Kanze wrote:

On Jun 25, 6:37 pm, "osmium" <r124c4u...@com cast.netwrote:

>"Isliguezze " wrote:

>
[...]

>The only ways I know of doing "Press any key" are
>non-standard. Only Microsoft would think that the up arrow
>key and it's cousins was not a key, so the message was wrong
>from the get-go.

>
I don't know about the up arrow key, but I've yet to see a
program which responded to the control key or the shift key in
such cases.
>
(Back in the old days, before anyone had even heard of the term
"computer literacy", you'd occasionally see such messages in
demo programs at technical fairs. At which point, I'd call one
of the sales droids over, and point out that the program wasn't
working by hitting the control key. Nine times out of ten, the
sales droid would then go off to find some technical support
person to fix it.)

I've actually written programs that did handle literally ANY key press.
More trouble than it was worth, and not portable in the slightest.

>
--
James Kanze (GABI Software) email:james.kan ze@gmail.com
Conseils en informatique orientée objet/
Beratung in objektorientier ter Datenverarbeitu ng
9 place Sémard, 78210 St.-Cyr-l'École, France, +33 (0)1 30 23 00 34

--
Daniel Pitts' Tech Blog: <http://virtualinfinity .net/wordpress/>

**Paavo Helde** · Jun 27 '08, 04:47 PM

Re: Two i/o questions

Daniel Pitts <newsgroup.spam filter@virtuali nfinity.netkirj utas:

I've actually written programs that did handle literally ANY key press.
More trouble than it was worth, and not portable in the slightest.

Just for curiosity - did this include the Del key press in a Ctrl+Alt+Del
combination on Windows?

Paavo

**Daniel Pitts** · Jun 27 '08, 04:47 PM

Re: Two i/o questions

Paavo Helde wrote:

Daniel Pitts <newsgroup.spam filter@virtuali nfinity.netkirj utas:

>I've actually written programs that did handle literally ANY key press.
> More trouble than it was worth, and not portable in the slightest.

>
Just for curiosity - did this include the Del key press in a Ctrl+Alt+Del
combination on Windows?
>
Paavo
>

It was a DOS program, but in any case it could have, as it implemented
the keyboard interrupt directly, bypassing BIOS handling.

--
Daniel Pitts' Tech Blog: <http://virtualinfinity .net/wordpress/>

Two i/o questions

Two i/o questions

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