Adding the combining overline unicode character - unicode

Question

I'm writing a program that converts an integer to a Roman numeral.
Roman numerals over 3999 are overlined, so IV overlined is 4000, CM overlined is 900'000, etc. These lines can stack.
So as to not limit my program, stopping it at just 3999 isn't good enough.
The question is, how do I add the "combining overline" unicode character to my string to achieve this?
My program is written in Rust, but I suspect the solution is similar across most languages that support unicode strings.

Answer 1

Just add the combining mark after each character.
Here's a Python example. What you see depends on support for combining marks in your console/IDE/browser.
with open('test.txt','w',encoding='utf-8-sig') as f:
print('I\u0305V\u0305',file=f)
Output (image and text)
(image) I̅V̅ (text)
In testing, U+0305 COMBINING OVERLINE could stack up to two, but Chrome drew incorrectly for three. There is also U+033F COMBINING DOUBLE OVERLINE.

Answer 2

You can just use them in string constants, either with the Unicode escape sequence (here shown for Rust) or directly (as they can be easily represented in UTF-8 source code files):
println!("I\u{0305}V\u{0305} - I̅V̅");
Note however, that each letter with overline requires two Unicode codepoints. So they do not fit into a single char. You need to use a string.
The combining overline character itself fits into a single character:
let combining_overline = '\u{0305}';
To apply it, insert it after the base character that needs the overline.