This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 110c. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.

2023-02-07


262. Default arguments and ellipsis

Section: 9.3.4.6  [dcl.fct]     Status: CD1     Submitter: Jamie Schmeiser     Date: 13 Nov 2000

[Voted into WP at April 2003 meeting.]

The interaction of default arguments and ellipsis is not clearly spelled out in the current wording of the Standard. 9.3.4.7 [dcl.fct.default] paragraph 4 says,

In a given function declaration, all parameters subsequent to a parameter with a default argument shall have default arguments supplied in this or previous declarations.

Strictly speaking, ellipsis isn't a parameter, but this could be clearer. Also, in 9.3.4.6 [dcl.fct] paragraph 2,

If the parameter-declaration-clause terminates with an ellipsis, the number of arguments shall be equal to or greater than the number of parameters specified.

This could be interpreted to refer to the number of arguments after the addition of default arguments to the argument list given in the call expression, but again it could be clearer.

Notes from 04/01 meeting:

The consensus opinion was that an ellipsis is not a parameter and that default arguments should be permitted preceding an ellipsis.

Proposed Resolution (4/02):

Change the following sentence in 9.3.4.6 [dcl.fct] paragraph 2 from

If the parameter-declaration-clause terminates with an ellipsis, the number of arguments shall be equal to or greater than the number of parameters specified.

to

If the parameter-declaration-clause terminates with an ellipsis, the number of arguments shall be equal to or greater than the number of parameters that do not have a default argument.

As noted in the defect, section 9.3.4.7 [dcl.fct.default] is correct but could be clearer.

In 9.3.4.7 [dcl.fct.default], add the following as the first line of the example in paragraph 4.

  void g(int = 0, ...);  // okay, ellipsis is not a parameter so it can follow
                         // a parameter with a default argument