What does “domain type” and “real type” mean?

Question

Quote from N1570:

6.3.1.8 Normal arithmetic conversions

1 Many operators expecting operands of arithmetic type, conversions, and result types of results in a similar way. The goal is to define a common real type for operands and result. For given operands, each operand is converted without changing the type , to type, the corresponding real type is a common real type. Unless otherwise indicated, a generic real type is also the corresponding real result type , whose type domain is the operand type domain if they are the same and otherwise complex. This pattern is called regular arithmetic conversion:

• First, if the corresponding real type of any operand is long double, the other operand is converted without changing the type of domain , to the type, the corresponding real type is long.
• Otherwise,......

What are "type domain" and "real type"? I am looking for a document, but no definition found.

Answer 1

6.2.5 Types of N1570 say the following:

Integer and floating types are collectively called arithmetic types. Each arithmetic type belongs to one domain of type : a domain of a real type contains real types , a domain type includes a complex of Types .

Further:

There are three real floating types , designated as float , double , and also long double . 42) A set of values ​​of type float is a subset of a set of values ​​of type double; a double value set is a subset of a long double value set

and

There are three complex types, designated as float _Complex , double _Complex and long double _Complex .

(note that the standard does not say anything about complex integer types, so all integer types defined in the standard belong to the domain of the real type).

Thus, it is clear that the field relates to mathematical concepts of real numbers ℝ and complex numbers ℂ .

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Basically what you read in your question is that if you, for example, add a real number with an imaginary number or a complex number, the result is also a complex number; and also that the operands advance to the width of the largest operand before the operation.