How to print unicode characters (no library)?

[Adam Ruppe]

On Sunday, 26 December 2021 at 20:50:39 UTC, rempas wrote:
> I want to do this without using any library by using the 
> "write" system call directly with 64-bit Linux.

write just transfers a sequence of bytes. It doesn't know nor 
care what they represent - that's for the receiving end to figure 
out.

> know (and tell me if I'm mistaken), UTF-16 and UTF-32 have 
> fixed size lengths for their characters.

You are mistaken. There's several exceptions, utf-16 can come in 
pairs, and even utf-32 has multiple "characters" that combine 
onto one thing on screen.

I prefer to think of a string as a little virtual machine that 
can be run to produce output rather than actually being 
"characters". Even with plain ascii, consider the backspace 
"character" - it is more an instruction to go back than it is a 
thing that is displayed on its own.

> Now the UTF-8 string will report 11 characters and print them 
> normally.

This is because the *receiving program* treats them as utf-8 and 
runs it accordingly. Not all terminals will necessarily do this, 
and programs you pipe to can do it very differently.

> Now what about the other two? I was expecting UTF-16 to report 
> 16 characters and UTF-32 to report 32 characters.

The [w|d|]string.length function returns the number of elements 
in there, which is bytes for string, 16 bit elements for wstring 
(so bytes / 2), or 32 bit elements for dstring (so bytes / 4).

This is not necessarily related to the number of characters 
displayed.

> Isn't the "write" system call just writing a sequence of 
> characters without caring which they are?

yes, it just passes bytes through. It doesn't know they are 
supposed to be characters...