Defect Report #116

Submission Date: 03 Dec 93
Submittor: WG14
Source: Ron Guilmette
Question
ANSI/ISO C Defect Report #rfg23:
Subject: Implicit unary & applied to register arrays.
a) Does the following code involve usage which requires a diagnostic from a conforming implementation?
b) Does the following code involve usage which renders the code itself not strictly conforming?
void example ()
{
register int array[5] = 0;

array; /* ? */
array[3]; /* ? */
array+3; /* ? */
}
Background:
Subclause 6.5.1 (footnotes):
The implementation may treat any register declaration simply as an auto declaration. However whether or not addressable storage is actually used, the address of any part of an object declared with storage-class specifier register may not be computed, either explicitly (by use of the unary & operator as discussed in 6.3.3.2) or implicitly (by converting an array name to a pointer as discussed in 6.2.2.1). Thus the only operator that can be applied to an array declared with storage-class specifier register is sizeof.
This footnote, while offering guidance, doesn't really answer the question of whether or not an implementation is required to issue a diagnostic for the case where the address of a register array is implicitly taken (as discussed in subclause 6.2.2.1). Nor does it definitively answer the question of whether such code should be considerd to be strictly conforming or not.
(Reference: CIB #1, RFI #17, question #6.)
Response
a) No, a diagnostic is not required.
b) Yes, this renders the program not strictly conforming.
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