Making terminal input send after a certain number of characters - c

I am creating a Linux terminal program using C.
I am trying to make a two digit code address a array location.
I don't want to have to hit enter after every two digit input, I want the input to just be sent to my buffer variable through scanf directly after to characters are entered.
I do not have a code sample, as i have no idea how to approach this.
Thanks for any help!

You've got two options, which solve the same problem in nearly the same way. The first is to use stdbuf when you run your program; the invocation is:
stdbuf -i0 ./a.out
Using that prevents stdin from being line-buffered, and will let you use fread() or similar commands to retrieve input as it happens.
The other is to put the terminal in raw mode. It's well-described here. But the downside is that control characters are no longer dealt with. In your program, you
#include <termios.h>
main(){
struct termios trm;
tcgetattr(STDIN_FILENO, &trm); /* get the current settings */
trm.c_cc[VMIN] = 1; /* return after 1 byte read; you might make this a 2*/
trm.c_cc[VTIME] = 0; /* block forever until 1 byte is read */
tcsetattr(STDIN_FILENO, TCSANOW, &trm);
}

Related

Switching back to Standard output after using ncurses WINDOW [duplicate]

I have been trying to get getch to work in another program with no success. So I have made the most basic program I can using getch the way I want it to work in the main program.
I have researched the need for noecho, cbreak, initscr and nodelay, I have also tried using newscr() but to no success.
The problem I am having is that the chars aren't being printed to the screen till I hit "enter", when they should be put to the screen every loop. Why is this happening? Also the cursor doesn't return to the left of the screen at the new line. eg.
abc
def
ghi
I have looked for the answer but am stumped again...
#include <stdio.h>
#include <ncurses.h>
int main()
{
initscr();cbreak(); noecho();nodelay(stdscr,0);
char c ;
while((c=getch())!=EOF){
putchar(c);}
return 0;
}
You're not seeing the output because your stdout stream is line buffered.
Your program is getting the individual characters all right; but the output stream is buffering them.
Try fflush(stdout); or switching stdout to unbuffered mode with setbuf(stdout, NULL);.
The problem with disabling buffering is that it's inefficient for bulk data processing when the output isn't a terminal.
You can make it conditional on the standard output being a tty:
if (isatty(fileno(stdout))) /* #include <unistd.h> */
setbuf(stdout, NULL);
To return the cursor to the start of the line, you need to put out a carriage return \r. This is because curses' cbreak mode has disabled the ONLCR tty mode (on Output, when sending NL add CR).
If you unconditionally add \r, then it will appear in files when your output is redirected. So again you need some isatty hack.
A much better might be to learn how to use the tcgetattr and tcsetattr functions to precisely control specific tty parameters, if all you want is to do character-at-a-time input without echo, and not actually develop an interactive curses-based program.
Do you really want character-at-a-time input, or just to diable echo? It's easy to disable echo. Call tcgetattr to fill a struct termios with the current settings of file descriptor 0 (if it is a tty). Flip some flags to turn off echoing, then call tcsetattr to install the updated structure. When your program exits, be nice and put back the original one. Done.
Yes, ncurses is a good way to get character-by-character control.
And yes, you must call "initscr()" and "cbreak()".
SUGGESTIONS:
1) Compare your code with this ncurses "hello world":
#include <ncurses.h>
int main()
{
initscr(); /* Start curses mode */
printw("Hello World !!!"); /* Print Hello World */
refresh(); /* Print it on to the real screen */
getch(); /* Wait for user input */
endwin(); /* End curses mode */
return 0;
}
2) See what happens if you do a "refresh()" and/or remove the "noecho()".
3) This tutorial has lots of good info that might also help:
http://tldp.org/HOWTO/NCURSES-Programming-HOWTO/

Why doesn't this program print one character at a time? [duplicate]

I have been trying to get getch to work in another program with no success. So I have made the most basic program I can using getch the way I want it to work in the main program.
I have researched the need for noecho, cbreak, initscr and nodelay, I have also tried using newscr() but to no success.
The problem I am having is that the chars aren't being printed to the screen till I hit "enter", when they should be put to the screen every loop. Why is this happening? Also the cursor doesn't return to the left of the screen at the new line. eg.
abc
def
ghi
I have looked for the answer but am stumped again...
#include <stdio.h>
#include <ncurses.h>
int main()
{
initscr();cbreak(); noecho();nodelay(stdscr,0);
char c ;
while((c=getch())!=EOF){
putchar(c);}
return 0;
}
You're not seeing the output because your stdout stream is line buffered.
Your program is getting the individual characters all right; but the output stream is buffering them.
Try fflush(stdout); or switching stdout to unbuffered mode with setbuf(stdout, NULL);.
The problem with disabling buffering is that it's inefficient for bulk data processing when the output isn't a terminal.
You can make it conditional on the standard output being a tty:
if (isatty(fileno(stdout))) /* #include <unistd.h> */
setbuf(stdout, NULL);
To return the cursor to the start of the line, you need to put out a carriage return \r. This is because curses' cbreak mode has disabled the ONLCR tty mode (on Output, when sending NL add CR).
If you unconditionally add \r, then it will appear in files when your output is redirected. So again you need some isatty hack.
A much better might be to learn how to use the tcgetattr and tcsetattr functions to precisely control specific tty parameters, if all you want is to do character-at-a-time input without echo, and not actually develop an interactive curses-based program.
Do you really want character-at-a-time input, or just to diable echo? It's easy to disable echo. Call tcgetattr to fill a struct termios with the current settings of file descriptor 0 (if it is a tty). Flip some flags to turn off echoing, then call tcsetattr to install the updated structure. When your program exits, be nice and put back the original one. Done.
Yes, ncurses is a good way to get character-by-character control.
And yes, you must call "initscr()" and "cbreak()".
SUGGESTIONS:
1) Compare your code with this ncurses "hello world":
#include <ncurses.h>
int main()
{
initscr(); /* Start curses mode */
printw("Hello World !!!"); /* Print Hello World */
refresh(); /* Print it on to the real screen */
getch(); /* Wait for user input */
endwin(); /* End curses mode */
return 0;
}
2) See what happens if you do a "refresh()" and/or remove the "noecho()".
3) This tutorial has lots of good info that might also help:
http://tldp.org/HOWTO/NCURSES-Programming-HOWTO/

Loop until user inputs an Integer, but skip the read in if no integer exists on the terminal

Im trying to create an application that will count pulses from an Oscilloscope, my problem is this:
I need a loop to run constantly, until a user input is entered. However I dont want getch() to be called unless there is an input on the terminal ready to be read. How would I go about checking for a character or integer existing on the terminal?
If you're coding for UNIX, you'll need to use either poll(2) or select(2).
Since you mention the non-standard getch you might also have kbhit which tests if there is input waiting. But don't slug your oscilloscope with that every loop: you can ease the flow by checking occasionally.
#include <conio.h>
#include <stdio.h>
#define POLLMASK 0xFFFF
int main(void){
int poll = 0;
int ch = 0;
while(ch != 27) {
// ... oscilloscope details
if ((poll++ & POLLMASK) == 0 && _kbhit()) {
ch = _getch();
// ... do something with input
}
}
return 0;
}
Use scanf() . It's standard, it already waits for a character in the buffer, and it's pretty much universal.
EDIT:
In the case of an unnamed OS, this is simply not to be done. Standard C has no way of reading raw data from a terminal and guaranteeing verbatim, unformatted results. It's entirely up to your terminal handler.
However, if your microcontroller has some sort of serial library, I would suggest doing something like this:
if characters in buffer is greater than 0, and the character just read is not a terminating character, report it. Otherwise, keep waiting for a character in the buffer.
until a user input is entered. this sentence indicates the user will use the keyboard eventually, therefore, you can track keyboard callback event to track the user's input. There are several libraries that provide you with such keyboard events (e.g. GLUT, SDL)

How can I flush unread data from a tty input queue on a UNIX system?

My program has to read just ONE character from the standard input, and so I use read(0, buffer, 1).
But if the user insert more than one single character, they remain in some buffer and when I call a read again they are still there.
So, how can I discard these characters?
I want that when I call a read again, the buffer is filled with the new character, not with the old ones.
An example:
I've a read(0, buffer, 1) and the user writes abcde. My buffer contains a (and it's right), but then I call read(0, buffer, 1) again and I want the next character written by the user from now, and not the b written before.
The POSIX answer is tcflush(): flush non-transmitted output data, non-read input data, or both. There is also tcdrain() which waits for output to be transmitted. They've been in POSIX since there was a POSIX standard (1988 for the trial-use version), though I don't recall ever using them directly.
Example program
Compile this code so the resulting program is called tcflush:
#include <stdio.h>
#include <unistd.h>
#include <termios.h>
int main(void)
{
char buffer[20] = "";
read(0, buffer, 1);
printf("%c\n", buffer[0]);
tcflush(0, TCIFLUSH);
read(0, buffer, 1);
printf("%c\n", buffer[0]);
tcflush(0, TCIFLUSH);
return 0;
}
Example dialog
$ ./tcflush
abc
a
def
d
$
Looks like what the doctor ordered. Without the second tcflush(), the shell complains that it can't find a command ef. You can place a tcflush() before the first read if you like. It wasn't necessary for my simple testing, but if I'd used sleep 10; ./tcflush and then typed ahead, it would make a difference.
Tested on RHEL 5 Linux on an x86/64 machine, and also on Mac OS X 10.7.4.
When your program wants to start reading characters, it must drain the buffer of existing characters and then wait to read the character.
Otherwise, it will read the last character entered, not the last character entered after right now.
Naturally, you do not need to do anything with the read characters; but, you do need to read them.

getch and putchar not working without return

I have been trying to get getch to work in another program with no success. So I have made the most basic program I can using getch the way I want it to work in the main program.
I have researched the need for noecho, cbreak, initscr and nodelay, I have also tried using newscr() but to no success.
The problem I am having is that the chars aren't being printed to the screen till I hit "enter", when they should be put to the screen every loop. Why is this happening? Also the cursor doesn't return to the left of the screen at the new line. eg.
abc
def
ghi
I have looked for the answer but am stumped again...
#include <stdio.h>
#include <ncurses.h>
int main()
{
initscr();cbreak(); noecho();nodelay(stdscr,0);
char c ;
while((c=getch())!=EOF){
putchar(c);}
return 0;
}
You're not seeing the output because your stdout stream is line buffered.
Your program is getting the individual characters all right; but the output stream is buffering them.
Try fflush(stdout); or switching stdout to unbuffered mode with setbuf(stdout, NULL);.
The problem with disabling buffering is that it's inefficient for bulk data processing when the output isn't a terminal.
You can make it conditional on the standard output being a tty:
if (isatty(fileno(stdout))) /* #include <unistd.h> */
setbuf(stdout, NULL);
To return the cursor to the start of the line, you need to put out a carriage return \r. This is because curses' cbreak mode has disabled the ONLCR tty mode (on Output, when sending NL add CR).
If you unconditionally add \r, then it will appear in files when your output is redirected. So again you need some isatty hack.
A much better might be to learn how to use the tcgetattr and tcsetattr functions to precisely control specific tty parameters, if all you want is to do character-at-a-time input without echo, and not actually develop an interactive curses-based program.
Do you really want character-at-a-time input, or just to diable echo? It's easy to disable echo. Call tcgetattr to fill a struct termios with the current settings of file descriptor 0 (if it is a tty). Flip some flags to turn off echoing, then call tcsetattr to install the updated structure. When your program exits, be nice and put back the original one. Done.
Yes, ncurses is a good way to get character-by-character control.
And yes, you must call "initscr()" and "cbreak()".
SUGGESTIONS:
1) Compare your code with this ncurses "hello world":
#include <ncurses.h>
int main()
{
initscr(); /* Start curses mode */
printw("Hello World !!!"); /* Print Hello World */
refresh(); /* Print it on to the real screen */
getch(); /* Wait for user input */
endwin(); /* End curses mode */
return 0;
}
2) See what happens if you do a "refresh()" and/or remove the "noecho()".
3) This tutorial has lots of good info that might also help:
http://tldp.org/HOWTO/NCURSES-Programming-HOWTO/

Resources