Is there syntax for declaring character literals in hexadecimal notation?

Question

Something like

const X: char = '0x10FFFC';

Answer 1

Yes, use \u{..}:

const X: char = '\u{10FFFC}';

Playground

One trick for this cases is play with the compiler. If you try the following code it will give you a nice hint about what to do for example:

const X: char = 0x10FFFC as char;

error: only `u8` can be cast into `char`
 --> src/lib.rs:1:17
  |
1 | const X: char = 0x10FFFC as char;
  |                 ^^^^^^^^^^^^^^^^ help: use a `char` literal instead: `'\u{10FFFC}'`
  |
  = note: `#[deny(overflowing_literals)]` on by default