chris@mimsy.umd.edu (Chris Torek) (05/02/90)
>In article <1990Apr24.000717.7882@cunixf.cc.columbia.edu> >gm@cunixd.cc.columbia.edu (Gary Mathews) writes: >>I want to do some computation and be able to stop by a key pressed by the >>user. (As I said already, this cannot be done *portably*. Given a definition for `key pressed' and `user', it can usually be done; and it can usually be done without resorting to writing assembly code, as I once did on VMS so as to bypass the Pascal runtime library....) In article <8281@cognos.UUCP> jimp@cognos.UUCP (Jim Patterson) writes: > ioctl( stdin->_file, FIONREAD, &count ); > count += stdin->_cnt; Be *very* careful with this: a. FIONREAD does not exist on all Unix systems, and on some of those on which it does exist, it does not quite work right; b. stdin probably does not have a _file and/or _cnt structure member on some machines. (If you disagree, try porting to 4.4BSD when it comes out. You may be unpleasantly surprised.) -- In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7163) Domain: chris@cs.umd.edu Path: uunet!mimsy!chris
martin@mwtech.UUCP (Martin Weitzel) (05/02/90)
In article <1990Apr30.182959.18254@cti-software.nl> pim@cti-software.nl (Pim Zandbergen) writes: [original q&a deleted] > >There is also way to find out if a key has been pressed in System V, >but it is an *ugly* way. If all keyboard input flows thru a central function of your program, it's rather clean - just read a character with timeout set to 0 seconds and store that character in a static variable. Use some impossible value in the static, if no "look ahead" character is available. It's not extremly hard to extend the look ahead to a buffer and count of the available characters or have an additional function to purge them. BTW: If someone request the above information from me, my first reaction is to ask back: "Why do want to do this"? If the one who asks comes from DOS-world, there's a good probability that it's rather a 'timed out read' what he or she wants, and if you let them you can bet they will write an idle loop until some input is available. A: Ohhh, how *incredibly slow* is this UNIX system compared to good old DOS I used before ... B: Let's see ... hmm <typing ps ... etc.>; Ehhm, what does this program called "humpfelgrumpf" that is running on the other virtual screen? A: Oh, not much really, gathers some statistical information, not much work at all, some few tenths of a second every thirty seconds. B: And in the meantime. A: Just looks if a key has been pressed. -- Martin Weitzel, email: martin@mwtech.UUCP, voice: 49-(0)6151-6 56 83
hsiegel@cvbnet.UUCP (Howard Siegel 4-2390 x4064) (05/09/90)
gm@cunixd.cc.columbia.edu (Gary Mathews) writes: >I want to do some computation and be able to stop by a key pressed by the >user. Turbo C has a function kbhit() and Turbo Pascal has keypressed(), >but what can be done with UNIX? I've looked into the stdin structure: I don't know about other flavors of UNIX, but SunOS has a function named "select" [horribly non-intuitive, in my opinion] that ought to do what you want. The "man" page follows. SELECT(2) SYSTEM CALLS SELECT(2) NAME select - synchronous I/O multiplexing SYNOPSIS #include <sys/types.h> #include <sys/time.h> int select (width, readfds, writefds, exceptfds, timeout) int width; fd_set *readfds, *writefds, *exceptfds; struct timeval *timeout; FD_SET (fd, &fdset) FD_CLR (fd, &fdset) FD_ISSET (fd, &fdset) FD_ZERO (&fdset) int fd; fd_set fdset; DESCRIPTION select() examines the I/O descriptor sets whose addresses are passed in readfds, writefds, and exceptfds to see if some of their descriptors are ready for reading, ready for writing, or have an exceptional condition pending. width is the number of bits to be checked in each bit mask that represent a file descriptor; the descriptors from 0 through width-1 in the descriptor sets are examined. Typically width has the value returned by getdtablesize(2) for the maximum number of file descriptors. On return, select() replaces the given descriptor sets with subsets consisting of those descriptors that are ready for the requested opera- tion. The total number of ready descriptors in all the sets is returned. The descriptor sets are stored as bit fields in arrays of integers. The following macros are provided for manipulat- ing such descriptor sets: FD_ZERO (&fdset) initializes a descriptor set fdset to the null set. FD_SET(fd, &fdset ) includes a particular descriptor fd in fdset. FD_CLR(fd, &fdset) removes fd from fdset. FD_ISSET(fd, &fdset) is nonzero if fd is a member of fdset, zero otherwise. The behavior of these macros is undefined if a descriptor value is less than zero or greater than or equal to FD_SETSIZE, which is normally at least equal to the maximum number of descriptors supported by the system. If timeout is not a NULL pointer, it specifies a maximum interval to wait for the selection to complete. If timeout is a NULL pointer, the select blocks indefinitely. To effect a poll, the timeout argument should be a non-NULL pointer, pointing to a zero-valued timeval structure. Any of readfds, writefds, and exceptfds may be given as NULL pointers if no descriptors are of interest. Selecting true for reading on a socket descriptor upon which a listen (2) call has been performed indicates that a subse- quent accept(2) call on that descriptor will not block. RETURN VALUE select() returns the number of ready descriptors that are contained in the descriptor sets, or -1 if an error occurred. If the time limit expires then select() returns 0. If select() returns with an error, including one due to an interrupted call, the descriptor sets will be unmodified. ERRORS An error return from select() indicates: EBADF One of the descriptor sets specified an invalid descriptor. EINTR A signal was delivered before any of the selected events occurred, or before the time limit expired. EINVAL A component of the pointed-to time limit is outside the acceptable range: t_sec must be between 0 and 10^8, inclusive. t_usec must be greater-than or equal to 0, and less than 10^6. EFAULT One of the pointers given in the call referred to a non-existent portion of the process' address space. SEE ALSO accept(2), connect(2), getdtablesize(2), gettimeofday(2), listen(2), read(2V), recv(2), send(2), write(2V) BUGS Although the provision of getdtablesize(2) was intended to allow user programs to be written independent of the kernel limit on the number of open files, the dimension of a suffi- ciently large bit field for select remains a problem. The default size FD_SETSIZE (currently 256) is somewhat larger than the current kernel limit to the number of open files. However, in order to accommodate programs which might poten- tially use a larger number of open files with select, it is possible to increase this size within a program by providing a larger definition of FD_SETSIZE before the inclusion of /usr/include/sys/types.h. select() should probably return the time remaining from the original timeout, if any, by modifying the time value in place. This may be implemented in future versions of the system. Thus, it is unwise to assume that the timeout pointer will be unmodified by the select() call. Sun Release 4.0.3 Last change: 25 March 1989 3