Test whether key is pressed without blocking on Linux - c++

Question

I'm searching how to test if a key is pressed. The test shouldn't block the program. I can use a little library if it is not too heavy, but unfortunately ncurses is too much of a dependency to bring in.

Answer 1

I found a solution :
int khbit() const
{
struct timeval tv;
fd_set fds;
tv.tv_sec = 0;
tv.tv_usec = 0;
FD_ZERO(&fds);
FD_SET(STDIN_FILENO, &fds);
select(STDIN_FILENO+1, &fds, NULL, NULL, &tv);
return FD_ISSET(STDIN_FILENO, &fds);
}
void nonblock(int state) const
{
struct termios ttystate;
tcgetattr(STDIN_FILENO, &ttystate);
if ( state == 1)
{
ttystate.c_lflag &= (~ICANON & ~ECHO); //Not display character
ttystate.c_cc[VMIN] = 1;
}
else if (state == 0)
{
ttystate.c_lflag |= ICANON;
}
tcsetattr(STDIN_FILENO, TCSANOW, &ttystate);
}
bool keyState(int key) const //Use ASCII table
{
bool pressed;
int i = khbit(); //Alow to read from terminal
if (i != 0)
{
char c = fgetc(stdin);
if (c == (char) key)
{
pressed = true;
}
else
{
pressed = false;
}
}
return pressed;
}
int main()
{
nonblock(1);
int i = 0;
while (!i)
{
if (cmd.keyState(32)) //32 in ASCII table correspond to Space Bar
{
i = 1;
}
}
nonblock(0);
return 0;
}
It works well. Thanks for helping me. I hope it will help someone :)

Answer 2

I don't know what exactly you are looking for.
I recently did a Proof-of-Concept reading from "raw" input device nodes here: boost::asio read from /dev/input/event0. The example is with mouse, but Linux Kernel unifies input devices so keyboard would be about the same.
All you need here is UNIX permissions to open/read the device files (you could create them out-of-/etc-tree if that's more convenient for your deployment style).
The sample shows full asynchronous processing of events
I have used bindings to XTest (libxtst) (actually to send keystrokes); I imagine that this may contain the features you need
Then there is XInput which (as far as I can tell) constitute the XOrg way to abstract the "raw" input device streams I described in the first option