Match only valid UTF-8 characters

Question

I'm writing an ncurses app with Rust.

When the user inputs a valid UTF-8 char (like ć, or some Asian letters), I want to build up a search string from it and print it to screen. Currently I have this:

use ncurses::*;

fn main() {
    ...
    let mut search_string = String::new();
    ...
    loop {
        let user_input = getch();
        match user_input {
            27 => break,
            KEY_UP => { ... },
            KEY_DOWN => { ... },
            KEY_BACKSPACE => { ... },
            _ => {
                search_string += &std::char::from_u32(user_input as u32).expect("Invalid char.").to_string();
                mvaddstr(0, 0, &search_string);
                app::autosearch();
            }
        }
    }
}

However, this catches all other keys, such as F5, KEY_LEFT, etc.

How can I match only valid UTF-8 letters?

when input can be utf8 characters, you should to use get_wch function, when it is possible — Pavel Stehule, Apr 19 '20 at 12:57
ANSI escape sequences are valid UTF-8 encoded strings though. — trent, Apr 19 '20 at 13:08
That might be because of Unicode grapheme clusters — characters that consist of _multiple_ unicode scalar values. I'm not sure if/how well ncurses supports them. — Aloso, Apr 20 '20 at 04:22

score 0 · Answer 1 · answered Apr 19 '20 at 11:35

0

If getch gives you a u8, you could collect subsequent key presses into a Vec<u8> and then call e.g. from_utf8 on each getch, handling the error as appropriate (see Utf8Error for more info).

answered Apr 19 '20 at 11:35

phimuemue

34,669
9
84
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I'm not sure how many times should I call `getch()`, and where. Is there like a null byte that `getch()` returns so I can stop calling `getch()` when I encounter such a thing? I think you really should show a code example. Thanks in advance. – adder Apr 19 '20 at 12:34
As a start, you could just call `from_utf8` on each char, and try to find out from the potential `Utf8Error` how often you need to call it. – phimuemue Apr 19 '20 at 16:13

score 0 · Answer 2 · answered Apr 19 '20 at 14:47

0

In C, you could call get_wch() instead of getch() -- it returns KEY_CODE_YES for KEY_* codes, while the actual key is stored to an address passed as a parameter. But I don't know how this translates to Rust.

answered Apr 19 '20 at 14:47

William McBrine

2,166
11
7

Match only valid UTF-8 characters

2 Answers2