How to Store Emojis in char8_t and Print Them Out in C++20?

Question

I just now heard about the existence of char8_t, char16_t and char32_t and I am testing it out. When I try to compile the code below, g++ throws the following error:

error: use of deleted function ‘std::basic_ostream<char, _Traits>& std::operator<<(basic_ostream<char, _Traits>&, char32_t) [with _Traits = char_traits<char>]’
    6 |         std::cout << U'😋' << std::endl;
      |                      ^~~~~

#include <iostream>

int main() {
  char32_t c = U'😋';

  std::cout << c << std::endl;

  return 0;
}

Additionally, why can't I put the emoji into a char8_t or char16_t? For example, the following lines of code don't work:

char16_t c1 = u'😋';
char8_t c2 = u8'😋';
auto c3 = u'😋';
auto c4 = u8'😋';

From my understanding, emojis are UTF-8 characters and should therefore fit into a char8_t.

Answer 1

emojis are UTF-8 characters

There is no such thing as a "UTF-8 character".

There are Unicode codepoints. These can be represented in the UTF-8 encoding, such that each codepoint maps to a sequence of one or more UTF-8 code units: char8_ts. But that means that most codepoints map to multiple char8_ts: AKA, a string. And Emojis are not among the 127 codepoints that map to a single UTF-8 code unit.

Emoji in particular can be built out of multiple codepoints, so even using UTF-32, you cannot guarantee that any emoji could be stored in a single char32_t codepoint.

It's best to treat these things as strings, not characters, at all times. Forget that "characters" even exist.