> there is no guarantee `char` is 8 bits, nor that it represents text, or even a particular encoding.

True, but sizeof(char) is defined to be 1. In section 7.6.2.5:

"The result of sizeof applied to any of the narrow character types is 1"

In fact, char and associated types are the only types in the standard where the size is not implementation-defined.

So the only way that a C++ implementation can conform to the standard and have a char type that is not 8 bits is if the size of a byte is not 8 bits. There are historical systems that meet that constraint but no modern systems that I am aware of.

[1] https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2023/n49...