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?

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.

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);

}

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

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

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

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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!