This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 117a. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.

2025-04-13

734. Are unique addresses required for namespace-scope variables?

[Voted into WP at March, 2010 meeting.]

Consider the following example:

    static const char test1 = 'x';
    static const char test2 = 'x';
    bool f() {
        return &test1 != &test2;
    }

Is f() allowed to return false? Can a smart optimizer alias these two variables, taking advantage of the fact that they are const, initialized to the same value, and thus can never be different in a well-defined program?

The C++ Standard doesn't explicitly specify address allocation of objects except as members of arrays and classes, so the answer would appear to be that such an implementation would be conforming.

This situation appears to have been the inadvertent result of the resolution of issue 73. Prior to that change, 7.6.10 [expr.eq] said,

Two pointers of the same type compare equal if and only if they... both point to the same object...

That resolution introduced the current wording,

Two pointers of the same type compare equal if and only if... both represent the same address.

Notes from the March, 2009 meeting:

The CWG agreed that this aliasing should not be permitted in a conforming implementation.

Proposed resolution (November, 2009):

1. Add the following as a new paragraph after 6.7.2 [intro.object] paragraph 5:

2. Change 7.6.2.2 [expr.unary.op] paragraph 3 as follows:

The result of the unary & operator is a pointer to its operand. The operand shall be an lvalue or a qualified-id. In the first case, if the type of the expression is “T,” the type of the result is “pointer to T.” In particular, the address of an object of type “cv T” is “pointer to cv T,” with the same cv-qualifiers. For a qualified-id, if the member is a static member of type “T”, the type of the result is plain “pointer to T.” If the member is a non-static member of class C of type T, the type of the result is “pointer to member of class C of type T.” [Example:...