This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 115d. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.

2024-10-26

499. Throwing an array of unknown size

[Voted into the WP at the March, 2009 meeting.]

According to 14.2 [except.throw] paragraph 3,

The type of the throw-expression shall not be an incomplete type, or a pointer to an incomplete type other than (possibly cv-qualified) void.

This disallows cases like the following, because str has an incomplete type (an array of unknown size):

    extern const char str[];
    void f() {
        throw str;
    }

The array-to-pointer conversion is applied to the operand of throw, so there's no problem creating the exception object, which is the reason for the restriction on incomplete types. I believe this case should be permitted.

Notes from the April, 2005 meeting:

The CWG agreed that the example should be permitted. Note that the reference to throw-expression in the cited text is incorrect; a throw-expression includes the throw keyword and is always of type void. This wording problem is addressed in the proposed resolution for issue 475.

Proposed resolution (October, 2006)

Change 14.2 [except.throw] paragraph 3 as indicated:

...The type of the throw-expression shall not If the type of the exception object would be an incomplete type, or a pointer to an incomplete type other than (possibly cv-qualified) void the program is ill-formed...