Public Comment Number PC-UK0108

ISO/IEC CD 9899 (SC22N2620) Public Comment

=========================================== 

Date: 1998-02-25
Author: N.M Maclaren
Author Affiliation: Self
Postal Address:
    University of Cambridge,
    Computer Laboratory,
    New Museums Site,
    Pembroke Street,
    Cambridge CB3 3QG,
    United Kingdom
E-mail Address: <nmm1@cam.ac.uk>
Telephone Number: +44 1223 334761
Fax Number:       +44 1223 334679
Number of individual comments: 1


Comment 1. 

Category: Normative change to existing feature retaining the original intent

Committee Draft subsection: 6.5.5.2

Title: Ill-definition in array declarators


Detailed description:

The current wording does not seem to exclude constructions like:

    void fred (double a[*][*], double b[sizeof(a)], double c[a[1][1]],
        double d[&a[1]-&a[0]]);

I cannot think of any conditions where the values of such undefined
calculations are critical to the behaviour of any strictly conforming
program, but I think that some clarification is needed.  There are two
options: to define that the sizes of arrays in declarations with function
prototype scope are not evaluated, and to forbid such use.  I suggest
the latter, adding the following:

    An identifier with a variable length array type of unspecified size
    may not be used in an expression.

[ It would be possible to relax that slightly, but I can think of no good
reason for doing so, and that restriction is short and sweet. ]