Q67036: ANSI Spec Says Taking Address of register Array is Not Allowed

Article: Q67036
Product(s): See article
Version(s): 6.00 6.00a | 6.00 6.00a
Operating System(s): MS-DOS | OS/2
Keyword(s): ENDUSER | S_QUICKC buglist6.00 buglist6.00a | mspl13_c
Last Modified: 19-JAN-1991

According to the ANSI specification, you may not explicitly or
implicitly compute the address of an object declared with register
storage-class. Yet, the C and QuickC compilers DO allow you to take
the address of such an array declared with register storage-class. The
only operator that should be allowed to be used with these types of
arrays is sizeof.

The sample code below should give an error according to ANSI but no
errors or warnings are generated.

Microsoft has confirmed this to be a problem in C versions 6.00 and
6.00a and QuickC versions 2.50 and 2.51 (buglist2.50 and buglist2.51).
We are researching this problem and will post new information here as
it becomes available.

Sample Code
-----------

void main(void)
{
    register int array[10]; /* declared w/register storage-class */
    int *ptr;

    /* According to ANSI, none of the following should be allowed */

    ptr = array;         /* implicit address computation of array */
    ptr = &array[0];     /* explicit address computation with '&' */
    ptr = array + 5;     /* computation based on address of array */
}

In Section 3.5.1 of the ANSI specification, there is a footnote (55)
that includes the following information:

    ...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) or implicitly (by converting an
    array name to a pointer). Thus the only operator that can be
    applied to an array with storage-class specifier register is
    sizeof.

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