RE: Unbuffered char reads from App from stdin (keyboard)
From: Steven Vacca <hidden>
Date: 2002-02-15 18:39:07
Mark,
Using some of your unbuf_getch() code inside a while (1)
loop, fgetc() still blocks until a '\n', then, with each iteration
of the loop, 1 char is returned from the fgetc() until all chars are
returned, then fgetc() blocks again.
Is there a way to get chars without blocking and waiting for
the '\n'?
Thanks,
ShutEyeThinkin
//*************************************************************************
***********
Mark's code:
Hi,
I found some examples on groups.google.com that I modified
to suite my needs. Try something like these:
int
unbuf_getch()
{
FILE *input;
int selected;
struct termios initial_settings;
struct termios new_settings;
if (!isatty(fileno(stdout))) {
fprintf(stderr,"You are not a terminal, OK.\n");
}
input = fopen("/dev/tty", "r");
if(!input) {
fprintf(stderr, "Unable to open /dev/tty\n");
exit(1);
}
tcgetattr(fileno(input),&initial_settings);
new_settings = initial_settings;
new_settings.c_lflag &= ~ICANON;
new_settings.c_lflag &= ~ECHO;
new_settings.c_cc[VMIN] = 1;
new_settings.c_cc[VTIME] = 0;
new_settings.c_lflag &= ~ISIG;
if(tcsetattr(fileno(input), TCSANOW, &new_settings) != 0) {
fprintf(stderr,"could not set attributes\n");
}
selected = fgetc(input);
tcsetattr(fileno(input),TCSANOW,&initial_settings);
fclose(input);
return selected;
}
int
kbhit()
{
int ret, c;
fd_set read_file_descr;
struct timeval timeout;
int debug_flag;
/* this could be a global */
debug_flag = 0;
/* this macro initializes the file descriptor read_file_descr to to be
the empty set */
FD_ZERO(&read_file_descr);
/* this macro adds fileno(stdin) to the file descriptor read_file_descr
*/
FD_SET(fileno(stdin), &read_file_descr);
timeout.tv_sec = 0;
timeout.tv_usec = 100;
/* int FD_SETSIZE macro is maximum number of filedescriptors that fd_set
can hold */
/* function select waits for specified filedescr. to have a signal */
/* last argument struct timeval *timeout */
ret = select(1, &read_file_descr, NULL, NULL, &timeout);
switch( ret ) /* 0 is timeout, -1 error (in errno), 1 = data */
{
case -1:
if( debug_flag )
fprintf(stdout, "select returned -1 error\n");
ret = 0;
break;
case 0:
if( debug_flag )
fprintf(stdout, "select returned 0 timeout\n");
ret = 0;
break;
case 1:
if( debug_flag )
fprintf(stdout, "SELECT returned=%d input\n", ret);
ret = 1;
break;
default:
if( debug_flag )
fprintf(stdout, "select returned=%d invalid\n", ret);
break;
}
/* test if user has data. this'll eat the first non-CR keys pressed */
if( FD_ISSET(fileno(stdin), &read_file_descr) )
{
c = getc(stdin);
if( debug_flag )
fprintf(stdout, "USER KEY=%d\n", c);
FD_CLR(fileno(stdin), &read_file_descr);
}
return ret;
}
Mark
--
[root@hjinc mclayton] /sbin/insmod stddisclaimer.o
-----Original Message----- From: Steven Vacca [mailto:svacca@valcom.com] Sent: Friday, February 15, 2002 10:10 AM To: LinuxEmbeddedMailList (E-mail) Subject: Unbuffered char reads from App from stdin (keyboard) App and Linux kernel 2.2.13 running on mpc860T. I would like to know the best way, from inside my GNU C App, to sense if there's a keyboard key pressed. Something similar to kbhit() in Microsoft C. I would like to have a particular thread execute a loop continuously and only when a key is present, do a getc() or getchar(), or gets(), and the like. What is the best way to accomplish this? Is there a way to make stdin unbuffered? Thanks, ShutEyeThinkin
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