Over the years I've had to do this on various Unix systems. The following C code will work under SuSE Linux and most POSIX compliant systems. --------------------------------------------------------------------- #include <stdio.h> #include <unistd.h> #include <string.h> #include <errno.h> #include <termios.h> void GetOne() { int rv; int fd = fileno(stdin); char ch; struct termios oldflags, newflags; /*********** Reset the terminal to accept unbuffered input ***/ /* get the current oldflags */ tcgetattr(fd, &oldflags); newflags = oldflags; /* set raw input, 1 second timeout */ newflags.c_cflag |= (CLOCAL | CREAD); newflags.c_lflag &= ~(ICANON | ECHO | ECHOE | ISIG); /* set the terminal to the newflags settings */ tcsetattr(fd, TCSANOW, &newflags); rv = read(fd, &ch, 1); /* restore the oldflags -- This is important otherwise * your terminal will no longer echo characters */ tcsetattr(fd, TCSANOW, &oldflags); } int main() { printf("Wait for a char: "); fflush(stdout); GetOne(); /* do this after resetting the terminal because * stdin and stdout should be the same pseudo terminal */ printf("\n"); /* simply return back to beginning of line */ return 0; } ---------------------------------- -- Jerry Feldman <gaf@blu.org> Boston Linux and Unix user group http://www.blu.org PGP key id:C5061EA9 PGP Key fingerprint:053C 73EC 3AC1 5C44 3E14 9245 FB00 3ED5 C506 1EA9

Jerry Feldman <gaf@blu.org> [Fri, 30 May 2003 22:15:29 -0400]:

...

void GetOne()

<nitpick> This isn't a valid Prototype in ISO C, because the compiler can't distinguish between an empty parameter list and K&R definitions. So it should be void GetOne(void) </nitpick> I would agree with your nitpick here, but C89 very specifically allows

On Sat, 31 May 2003 05:49:51 +0200 Philipp Thomas <philipp.thomas@t-link.de> wrote: this. However, this was a quick hack. My copy of the ANSI specification, section 3.7.1 defines this. Also look at footnote 79 that has a specific example of an empty parameter list. (Note that the ISO version of the spec may have a different section number. My copy of C98 is a draft copy and is not at my fingertips).

...

int main()

<nitpick> Same here, this should be int main (void) </nitpick> Main is rarely used with a void argument list, but I guess it is more correct to specify void.

And you should have added that on Linux this needs to be linked against libncurses to get the lowlevel termio functions. Not true. Termios(3) is not dependent upon libncurses at all. I think you are confusing termio with termios. Check the man page for termios. The termios functions are in libc. gaf@gaf:~/src> nm /usr/lib/libncurses.a | grep tcgetattr U tcgetattr Note that this is an external reference. gaf@gaf:~/src> nm /usr/lib/libc.a | grep tcgetattr U __tcgetattr tcgetattr.o: 00000000 T __tcgetattr 00000000 W tcgetattr U __tcgetattr

In this case, in libc, tcgetattr is a weak symbol and __tcgetattr is the actual function name. -- Jerry Feldman <gaf@blu.org> Boston Linux and Unix user group http://www.blu.org PGP key id:C5061EA9 PGP Key fingerprint:053C 73EC 3AC1 5C44 3E14 9245 FB00 3ED5 C506 1EA9

On Sat, 31 May 2003 16:08:49 +0200 Philipp Thomas <philipp.thomas@t-link.de> wrote:

I should have been more precise, sorry. At least C89 allows it (can't check ISO C98 as it's at work). It's the compiler that can't distinguish between empty parameter list and K&R definition and thus won't flag passing parameters as an error. This is true to some extent. A good compiler should be able to catch the error in some cases. Lint on Tru64 Unix was able to do it, and it used a YACC parser. It is relatively easy for the compiler if the function is defined first. But, I don't think that gcc has that capability.

That's why I *always* change code to use void and have caught a few bugs in packages where functions first took a parameter and later none but as there was only a K&R prototype the compiler didn't catch it. It is a good practice to always use ANSI prototypes and ANSI function definitions. The only exception might be main() which is a special case in that it takes either 0 or 2 parameters (or 3 in archaic cases).

In C++, an empty parameter list is equivalent to using void as the parameter list since C++ does not permit K&R function types. But, other than the howto, in answer to the original person's question, "s read() evil in usermode", the answer is no. It is appropriate to use standard Unix/Linux system calls in any code that is intended for use in a Unix-like system. My only comment is that it is better to use the more portable interfaces, which is why I used termios(3) and not ioctl(2). Additionally, read(2), write(2), open(2) and close(2) are normally available in non-Unix systems. -- Jerry Feldman <gaf@blu.org> Boston Linux and Unix user group http://www.blu.org PGP key id:C5061EA9 PGP Key fingerprint:053C 73EC 3AC1 5C44 3E14 9245 FB00 3ED5 C506 1EA9

This is arrises a new question, since both using read() or using termio to put the terminal out of cooked mode solve the problem, using which of this builds up a better coding style, or better said: the correct coding style. First, these function make for somewhat unportable code. The code that I

On Sun, 1 Jun 2003 11:03:20 -0400 (PYT) Raúl Gutiérrez Segalés <rau@campoalto.edu.py> wrote: presented should work on most Unix and Linux systems (except maybe SCO), but on Windows, you might want to use the conio functions. As I created a separate function to wait for a keypress, it is best to make non-portable code into separate entities such that you can easily add that functionality on another platform. (by separate entity, I mean a separate function or macro). -- Jerry Feldman <gaf@blu.org> Boston Linux and Unix user group http://www.blu.org PGP key id:C5061EA9 PGP Key fingerprint:053C 73EC 3AC1 5C44 3E14 9245 FB00 3ED5 C506 1EA9

<nitpick> This isn't a valid Prototype in ISO C, because the compiler can't distinguish between an empty parameter list and K&R definitions. So it should be void GetOne(void) </nitpick> In any case, I decided to make a slight change to the function. It would be more useful for the function to take the file descriptor as the

On Sat, 31 May 2003 05:49:51 +0200 Philipp Thomas <philipp.thomas@t-link.de> wrote: parameter where the original function assumed that stdin was the input device. This function can be applied to any arbitrary input terminal device. Note I added the tcflush(3) function. Also, note that there is no error checking. ------------------------------------------ #include <stdio.h> #include <unistd.h> #include <string.h> #include <errno.h> #include <termios.h> void GetOne(int fd) { int rv; char ch; struct termios oldflags, newflags; /*********** Reset the terminal to accept unbuffered input ***/ /* get the current oldflags */ tcgetattr(fd, &oldflags); /* make a copy of the flags so we can easily restore them */ newflags = oldflags; /* set raw input */ newflags.c_cflag |= (CLOCAL | CREAD); newflags.c_lflag &= ~(ICANON | ECHO | ECHOE | ISIG); /* set the newflags */ tcsetattr(fd, TCSANOW, &newflags); rv = read(fd, &ch, 1); /* Flush the input queue. This takes into account the case * where an F button is pressed */ tcflush(fd, TCIFLUSH); /* restore the oldflags -- This is important otherwise * your terminal will no longer echo characters */ tcsetattr(fd, TCSANOW, &oldflags); } int main(void) { printf("Wait for a char: "); fflush(stdout); GetOne(fileno(stdin)); /* do this after resetting the terminal because * stdin and stdout should be the same pseudo terminal */ printf("\n"); /* simply return back to beginning of line */ return 0; } --------------------------------------------------- -- Jerry Feldman <gaf@blu.org> Boston Linux and Unix user group http://www.blu.org PGP key id:C5061EA9 PGP Key fingerprint:053C 73EC 3AC1 5C44 3E14 9245 FB00 3ED5 C506 1EA9