J3/00-284

To:      J3
From:    /Interop
Date:    19 Sep 2000
Subject: Issues with Bind(C) Enum Interoperability

Introduction.

It is not currently clear how the Enum BIND(C) interface produces C
interoperability in the case where the enumeration values can be represented
as unsigned values but not as signed values of the same length.

A C compiler is permitted to use an unsigned type for the representation of
an enumeration type 6.7.2.2(4).

Fortran can only use a signed type for the representation. As a result,
Fortran would need to use a wider type than is used by C. It currently
appears to be unclear how this case is handled.

To clarify the operation of BIND(C) enums, we propose to add a note to 4.7
clarifying this question. In addition, the note at 16.5 is edited to notice
explicitly that values may be interpreted differently in Fortran and in C.

Edits

58:39 Insert the following Note:

Note 4.x
If a companion processor uses an unsigned type to represent a given
enumeration type, the Fortran processor will use the signed integer type of
the same width for the enumeration even though some of the values of the
enumerators cannot be represented in this signed integer type. The values of
any such enumerators will be interoperable with the values declared in the C
enumeration.

389:21 Insert at the end of note 16.5

Values that can be represented in an unsigned type but not in the
corresponding signed type are represented by different values.