faq: cached input with mygetch()

ichijoji · 04-07-2004, 12:17 PM

So I'm trying to put together a little text game at school on their redhat machines, right? I'm using a char buffer with system("clear") to write to the screen and mygetch() from the faq to get input.

Code:

int mygetch() {
  struct termios oldt,
                 newt;
  int            ch;
  tcgetattr( STDIN_FILENO, &oldt );
  newt = oldt;
  newt.c_lflag &= ~( ICANON | ECHO );
  tcsetattr( STDIN_FILENO, TCSANOW, &newt );
  ch = getchar();
  tcsetattr( STDIN_FILENO, TCSANOW, &oldt );
  return ch;
}

This function does what I need, except it waits for keyboard input before returning a value. Is there any way to get it to return like 0 or something when there's no input, or maybe a whole other function that does that?

**Thantos** · 04-07-2004, 12:37 PM

Hmm not sure if there is a kbhit() for linux or not. But you could use select() on stdin to find out when there is input, however I think that requires the enter key. Might want to change the program to use raw input all the way through and then switch it back before exiting.

**Thantos** · 04-07-2004, 01:46 PM

Good news

If you change it to raw mode then you select will work without the enter key:

Test program:

Code:

#include <stdio.h>
#include <termios.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/time.h>

void changemode(int);
int  kbhit(void);
int main(void)
{
  int ch;
  changemode(1);
  while ( !kbhit() )
  {
    putchar('.');
  }

  ch = getchar();

  printf("\nGot %c\n", ch);

  changemode(0);
  return 0;
}

void changemode(int dir)
{
  static struct termios oldt, newt;

  if ( dir == 1 )
  {
    tcgetattr( STDIN_FILENO, &oldt);
    newt = oldt;
    newt.c_lflag &= ~( ICANON | ECHO );
    tcsetattr( STDIN_FILENO, TCSANOW, &newt);
  }
  else
    tcsetattr( STDIN_FILENO, TCSANOW, &oldt);
}

int kbhit (void)
{
  struct timeval tv;
  fd_set rdfs;

  tv.tv_sec = 0;
  tv.tv_usec = 0;

  FD_ZERO(&rdfs);
  FD_SET (STDIN_FILENO, &rdfs);

  select(STDIN_FILENO+1, &rdfs, NULL, NULL, &tv);
  return FD_ISSET(STDIN_FILENO, &rdfs);

}

I'm sure there can be improvements but hey it works

awoodland · 04-27-2004, 05:50 AM

To make this work on Solaris you might also find you need the following:

Code:

	newt.c_lflag &= ~(ICANON|ECHO|IEXTEN);
	/* also set TIME to 0 and MIN to 1 (getc will block until there 
	     is atleast 1 char avalible, and return as soon as there is)*/
	newt.c_cc[VTIME] = 0;
	newt.c_cc[VMIN] = 1;

IEXTEN is a implementation defined extension which seems to be on by default on Solaris and makes bad things (tm) happen, and also Solaris seems to default to VMIN being 4 (haven't actualy confirmed it is 4, but it felt like that, and this fixed it)

Alan

cniggeler · 06-18-2008, 11:36 PM

Quote:

Originally Posted by awoodland

To make this work on Solaris you might also find you need the following:

Code:

	newt.c_lflag &= ~(ICANON|ECHO|IEXTEN);
	/* also set TIME to 0 and MIN to 1 (getc will block until there 
	     is atleast 1 char avalible, and return as soon as there is)*/
	newt.c_cc[VTIME] = 0;
	newt.c_cc[VMIN] = 1;

IEXTEN is a implementation defined extension which seems to be on by default on Solaris and makes bad things (tm) happen, and also Solaris seems to default to VMIN being 4 (haven't actualy confirmed it is 4, but it felt like that, and this fixed it)

Alan

Man, thanks for that! I can confirm that the VMIN item needs to be set if compiling on HPUX/Itanium (but not for other OSes like Linux); otherwise, you have to press a key exactly 4 times before one gets recognized!

04-07-2004, 12:17 PM	#1
ichijoji GA Join Date: Nov 2002 Posts: 179	faq: cached input with mygetch() So I'm trying to put together a little text game at school on their redhat machines, right? I'm using a char buffer with system("clear") to write to the screen and mygetch() from the faq to get input. Code: int mygetch() { struct termios oldt, newt; int ch; tcgetattr( STDIN_FILENO, &oldt ); newt = oldt; newt.c_lflag &= ~( ICANON \| ECHO ); tcsetattr( STDIN_FILENO, TCSANOW, &newt ); ch = getchar(); tcsetattr( STDIN_FILENO, TCSANOW, &oldt ); return ch; } This function does what I need, except it waits for keyboard input before returning a value. Is there any way to get it to return like 0 or something when there's no input, or maybe a whole other function that does that? __________________ Illusion and reality become impartiality and confidence. Last edited by ichijoji; 04-07-2004 at 12:19 PM.
ichijoji is offline

04-07-2004, 12:37 PM	#2
Thantos & the hat of GPL slaying Join Date: Sep 2001 Posts: 5,732	Hmm not sure if there is a kbhit() for linux or not. But you could use select() on stdin to find out when there is input, however I think that requires the enter key. Might want to change the program to use raw input all the way through and then switch it back before exiting.
Thantos is offline

04-27-2004, 05:50 AM	#4
awoodland Registered User Join Date: Apr 2004 Posts: 9	To make this work on Solaris you might also find you need the following: Code: newt.c_lflag &= ~(ICANON\|ECHO\|IEXTEN); /* also set TIME to 0 and MIN to 1 (getc will block until there is atleast 1 char avalible, and return as soon as there is)*/ newt.c_cc[VTIME] = 0; newt.c_cc[VMIN] = 1; IEXTEN is a implementation defined extension which seems to be on by default on Solaris and makes bad things (tm) happen, and also Solaris seems to default to VMIN being 4 (haven't actualy confirmed it is 4, but it felt like that, and this fixed it) Alan
awoodland is offline

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