If have just been writing a lot of C code to support unicode in a new project. It reads UTF-8 converts to UTF-32 does lots of clever stuff and spits UTF-8 out once again.

Here's my take: UTF-8 should, rightly, be the only interchangeable text format of choice for the right-minded individual. The other UTFs should be internal formats used in-memory or on disk cache / database / etc

Why? Simple: UTF-8 rocks!

It's a beautifully designed, backwardly compatible, nifty piece of back-of-a-napkin genius. Simple to code and decode (once you understand it), simple to check with a regular expression (once you realise it is essentially just a token with a set number of chars), and simple to add the wealth of the world's characters to your app with a reasonable amount of code. Plus, it's compact in the way Huffman coding is compact (at least from a western perspective).

Also, no-one should ever be using (char ❄) in the 21st century unless it is to temporarily hold a UTF-8 string before converting to wchar.

Why? Because you almost certainly don't have a (char ❄), you have a UTF-8 sequence (^^^see above). Sadly this makes your memory mapped files slightly redundant. But don't fret, this is the future: convert them to 32-bits and release them. Be happy that you can now treat any character sequence, in common usage, in the whole of humanity like an array.

As for UTF-16, why bother? It's neither compact, clever, nor big enough to hold every character on the internet. 💩 needs more than 16 bits and everyone, now, needs to support a poop with eyes.

tl;dr: Share UTF-8 promiscuously, keep UTF-32 for private moments. Don't dally with UTF-16, she's an old tease and can't handle poop.

note: ❄ = asterisk :)