bright dim Colors, backgrounds underscore, blink.Double width line echo $'\e'#5abcdefg echo $'\e'#6abcdefg.␛ lead-in required by many ANSI terminal control strings. In this document the symbol £ indicates sequences supported by £inux TERM=ansiįrom the bash command line echo $'\e' outputs the These sequences are usually implemented in the terminal emulator in the system's BIOS (?) andĪre available in DOS, linux console, windows command modes and mac os terminal.Ĭurses are involved in displaying character sequences. While ((nbytes = read(fd, keys, sizeof(keys))) > 0)ANSI terminal control strings used with terminal emulators ANSI standards for ASCII terminals Joe Smith, 18-May-84, * These two need to be set in main() but accessed from reset_tty() */Ītexit(reset_tty) // Ensure the terminal is reset whenever possible So, this mainly shows a couple of extra techniques, but it could be useful as an alternative way of thinking about the processing. You'd need to add sleep code somewhere to allow characters to accumulate before it reads them. Good luck in demonstrating that with this program as written - you're not a fast enough typist. There's also a chance that the ESC from a function key or arrow key will be the last character that fits in the buffer - in which case, extra reading is necessary. because the program was computing while input was accumulating). The only downside to this is that the buffer must be available where characters need to be read in the unlikely event that several characters are read (e.g. I use an array of length 4 since I think that's longer than the longest key sequence generated from the keyboard I'd be happy to increase it to 8 (or any other larger number). In practice, the computer is hugely faster than a mere human, so it either reads a single character or the complete sequence. If it doesn't find any more characters, it uses select() as before to decide whether there are more characters in an ESC sequence or if this is a standalone ESC. If it finds one and there is any data left, then it reports the escape sequence (presumably a function key sequence). If the code reads multiple characters, it scans through them, looking for ESC (escape). (We can debate whether the code should also use the at_quick_exit() function - it's a feature of C11 but not of POSIX.) I also use the atexit() function to do most of what can be done to ensure that the terminal attributes are reset to the sane state even if the program doesn't exit via the main() program. There are two nested loops, so I use a goto end_loops (twice!) to break out of the both loops from the inner loop. This code reads up to 4 characters at a time, and processes those that are received. Other characters seem plausible, the code was rigged to break when control-D is pressed. I pressed the left/right arrow keys and got 'possible sequence' reported I pressed the ESC on the touch strip and got 'ESC key standalone'. Printf("error %d: %s\n", errno, strerror(errno)) #include įprintf(stderr, "%d (control-D or EOF)\n", key) Here's a straight-forward adaptation of your code (tested on a MacBook Pro running macOS High Sierra 10.13.2), that produces the answer you and I want. I think the problem is that you're using getchar() - a function from the standard I/O library - where you need to use file descriptor I/O ( read()). Int selret = select(1, &set, NULL, NULL, &timeout) Įnter a key to see the ASCII value press x to exit. Printf("Enter a key to see the ASCII value press x to exit.\n") loop: get keypress and display (exit via 'x') I am running this on both MacOS High Sierra and Ubuntu 16 with equal results. Why doesn't select return anything except 0 in my example? Is it possible to check if stdin is empty? How do other libraries handle this? Minimal, Complete, and Verifiable Example Neither of those things happens, so I'm afraid I just don't understand select or standard in/out like I thought I did. I figured that if I typed →, then I would get a 1 returned since it sees that right after 27 there is a 91 and a 67 to read.I figured that if I didn't type anything after hitting Esc, then it would return -1 since it doesn't see anything left in stdin to read.Select always seems to return 0 (timeout expires). To that end, I'm trying to use select to see if stdin is empty or not. Wait some arbitrary amount of time to see if something comes in (seems hacky). I think I understand there are two options: I am using termios to put my terminal into non-Canonical mode. My end goal is to distinguish between my pressing Esc (ASCII 27) on my keyboard, and me pressing the → key on my keyboard (which translates to a sequence of 27 91 67).
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