_ Kbhit () forLinux-general Linux technology-Linux programming and kernel information. For details, refer to the following section. The Windows _ kbhit () function returns a nonzero value when a character is waiting in stdin, otherwise it returns zero. it does not consume the character and does not block. A common use of this function is to test when the user has pressed a key in an interactive console application. POSIX (and therefore Linux) lacks a similar function. although it does not directly support this functionality, the GNU Curses library can be used to implement _ kbhit () on Linux. here I present an alternate solution to Curses that implements _ kbhit () using only standard libraries. it shoshould port directly to OS X, AIX, and other Unix-like operating systems as well as Linux. this implementation has two advantages over a Curses based approach. the Curses library must be initialized from main () before it can be used. this implementation is a drop-in replacement for _ kbhit () when porting from Windows and does not require any explicit initialization. also, no external library must be installed and linked.
The ioctl () function is a low level method for controlling I/O drivers. its arguments depend on the stream and driver being used. the last group of lines in _ kbhit () uses this function to determine whether data is waiting on stdin. this implementation was written specifically for Linux and may not port. A more general implementation can replace these lines with a call to the select () function as follows:
Timeval timeout;
Fd_set rdset;
FD_ZERO (& rdset );
FD_SET (STDIN, & rdset );
Timeout. TV _sec = 0;
Timeout. TV _usec = 0;
Return select (STDIN + 1, & rdset, NULL, NULL, & timeout );
Console input is typically line buffered on Linux, special when running over Telnet or SSH. this means that a keypress does not appear on stdin until a newline character is sent. the ioctl () or select () CILS cannot determine if characters are in the buffer waiting for a newline, and can indicate that there are zero characters waiting when really several keys have been pressed.
To fix this, the first code block in _ kbhit () disables line buffering. this uses routines from the termios. h header. another author offers a longer method that uses only ioctl () and avoids termios. h. because termios. h is a standard header on most systems I see no reason to avoid it. both implementations use a static variable to detect the first call and disable buffering then. output buffering on stdout is still enabled. if you wish to print to stdout and see the result before a newline is sent, use the command flush (stdout) as shown in the simple demo.
The Linux version of _ kbhit () now performs to the same specification as the Windows version. The actual value of the non-zero integer returned will be different on the two platforms, however.
CODE :/**
Linux (POSIX) implementation of _ kbhit ().
Morgan McGuire, morgan@cs.brown.edu
*/
# Include
# Include
# Include
# Include Int _ kbhit (){
Static const int STDIN = 0;
Static bool initialized = false; if (! Initialized ){
// Use termios to turn off line buffering
Termios term;
Tcgetattr (STDIN, & term );
Term. c_lflag & = ~ ICANON;
Tcsetattr (STDIN, TCSANOW, & term );
Setbuf (stdin, NULL );
Initialized = true;
} Int bytesWaiting;
Ioctl (STDIN, FIONREAD, & bytesWaiting );
Return bytesWaiting;
}/////////////////////////////////////// ///////
// Simple demo of _ kbhit ()
# Include Int main (int argc, char ** argv ){
Printf ("Press any key ");
While (! _ Kbhit ()){
Printf (".");
Fflush (stdout );
Usleep (1000 );
}
Printf ("\ nDone. \ n"); return 0;
} |
