Question

[C++11: 1.7] talks about bytes in terms of bits:

The fundamental storage unit in the C++ memory model is the byte. A byte is at least large enough to contain any member of the basic execution character set (2.3) and the eight-bit code units of the Unicode UTF-8 encoding form and is composed of a contiguous sequence of bits, the number of which is implementation-defined. The least significant bit is called the low-order bit; the most significant bit is called the high-order bit. The memory available to a C++ program consists of one or more sequences of contiguous bytes. Every byte has a unique address.

However, I cannot find anywhere in the standard that defines “bit”.

So is it true to say that C++ does not place limitations on the number of values that may be represented by a single bit?

Does it allow, say, tri-state bits?

Answer 1

3.9.1.7 says

Types bool, char, wchar_t, and the signed and unsigned integer types
are collectively called integral types.48) A synonym for integral type
is integer type. The representations of integral types shall define
values by use of a pure binary numeration system.49) [ Example: this
International Standard permits 2’s complement, 1’s complement and
signed magnitude representations for integral types. — end example ]”

The note 49 reads

A positional representation for integers that uses the binary digits 0
and 1, in which the values represented by successive bits are
additive, begin with 1, and are multiplied by successive integral
power of 2, except perhaps for the bit with the highest position.
(Adapted from the American National Dictionary for Information
Processing Systems.)