How to determine end of std::cin

[Johannes Meng]

Good day,

I'm experimenting with unbuffered input at the moment. To get input I
basically use cin.get(). My problem are control sequences preceeded by an
ESC character (i.e. up, down, f-keys et cetera). They basically look like
this: <ESC><EXCODE><CODE>, where EXCODE is a number describing the type of
key pressed and CODE is the actual key. I want to be able to decide whether
ESC or such a control key was pressed. Now if I do it like this:

char code = 0, excode = 0;
code = cin.get()
if (code == 27) {
excode = cin.get();
code = cin.get();
}

, then I will have proper codes for all control keys. If ESC is pressed,
though, the user will actually have to press three times - because
cin.get() seems to wait for actual input to appear in stdin.
Now I tried stuff like

char code = 0, excode = 0;
code = cin.get()
if (code == 27 && !cin.eof()) {
excode = cin.get();
code = cin.get();
}

, but that won't work, even if there is only the ESC character in stdin.

Is there another way to determine, whether the last character was read
from stdin? Am I doing anything wrong?

Thanks alot.

 

[kwikius]

First, I'm no expert on standard keryboard input in C++.

However AFAIK std::cin is quite primitive and only accepts ASCII
characters. The characters you want are extended ASCII AFAIK and a
quick test on win32 seems to suggest that standard input simply
ignores them.

Unfortunately the proper way forward I think, is to start
investigating a GUI toolkit. These firstly use a different paradigm
from the "input as file" paradigm of standard C++. This is the event
based program paradigm, in which your application sits idling and the
system fires events at it to which it responds. Typical events are
mouse move and keyboard events , and you then write functions to
describe what your application should do in response.

The simplest way to try some event based programming I would guess is
to use another language such as Java. C++ has ( nor probably will ever
have) much interest in standardisng a GUI.

regards
Andy Little

 

[Johannes Meng]

First, I'm no expert on standard keryboard input in C++.

However AFAIK std::cin is quite primitive and only accepts ASCII
characters. The characters you want are extended ASCII AFAIK and a
quick test on win32 seems to suggest that standard input simply
ignores them.

Well, I don't know about win32, but here on linux, when, say, "arrow up" is
pressed, cin actually contains 27 91 65. Try the following:

#include <iostream>
using namespace std;

int main(int argc, char **argv)
{
string test;
cin >> test;

for (int i = 0; i < test.length(); i++) {
cout << (int)test << " ";
}

cout << endl;

return 0;
}

If you start the programm, then press "arrow up" and then "enter", it should
output "27 91 65".

That means that the codes are there - I just need a way to determine whether
there's still something left in cin after reading a 27 (code for esc).

 

[Johannes Meng]

The simplest way to try some event based programming I would guess is
to use another language such as Java. C++ has ( nor probably will ever
have) much interest in standardisng a GUI.

I just noticed I might not have been clear about what I want: I do _not_
want to program a gui. It's all about the command line

 

[kwikius]

#include <iostream>
using namespace std;

int main(int argc, char **argv)
{
string test;
cin >> test;

for (int i = 0; i < test.length(); i++) {
cout << (int)test << " ";
}

cout << endl;

return 0;

}

If you start the programm, then press "arrow up" and then "enter", it should
output "27 91 65".

Aha . Works when I compile using gcc (in Windows) but in VC7.1 hangs
when I press arrow up) until I press an ascii character.

Not sure whether there is a right and wrong or if its implementaion
defined. I suspect implementation defined though.

The one common characteristic is that you have to press return to
flush the buffer and signal end of input AFAIK, before you can make
anything happen.

And to avoid that ( I think) you need to be able to monitor system
events ( e.g in a loop looking for e.g any new key pressed etc) which
isnt provided for in a standardised form in C++

Again though I'm no expert on this...

regards
Andy Little.

 

[Alf P. Steinbach]

* Johannes Meng:

I just noticed I might not have been clear about what I want: I do _not_
want to program a gui. It's all about the command line

*Dragging up memories from the eighties*

You probably need to do input at a lower, system-specific level because
you need a timeout.

You should check whether there's some library that translates escape
sequences to something more digestible, not sure if 'curses' does that.

 

[Johannes Meng]

Aha . Works when I compile using gcc (in Windows) but in VC7.1 hangs
when I press arrow up) until I press an ascii character.

Not sure whether there is a right and wrong or if its implementaion
defined. I suspect implementation defined though.

The one common characteristic is that you have to press return to
flush the buffer and signal end of input AFAIK, before you can make
anything happen.

And to avoid that ( I think) you need to be able to monitor system
events ( e.g in a loop looking for e.g any new key pressed etc) which
isnt provided for in a standardised form in C++

Again though I'm no expert on this...

Thanks for testing! Well, I use unbuffered input, thus there's no need to
press enter. That works using some stuff from termios.h, which is most
probably linux/unix(?) specific, though.

 

[Johannes Meng]

*Dragging up memories from the eighties*

Hehe. That's about where I'm going ;P

You probably need to do input at a lower, system-specific level because
you need a timeout.

You should check whether there's some library that translates escape
sequences to something more digestible, not sure if 'curses' does that.

The thing is this: I'm currently coding an input prompt with bash-like
editing capabilities, history and so on. It's almost functional and really,
really small and I'd rather it didn't have any external dependencies. I'll
try looking for a suitable library anyways.

Thank you!

 

[kwikius]

Thanks for testing! Well, I use unbuffered input, thus there's no need to
press enter. That works using some stuff from termios.h, which is most
probably linux/unix(?) specific, though.

Yes look like a Unix header to me:

http://www.opengroup.org/onlinepubs/007908799/xsh/termios.h.html

regards
Andy Little