Defect Report #259

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Submitter: UK C Panel
Submission Date: 2001-09-07
Source: Clive D.W. Feather <>
Version: 1.1
Date: 2002-03-06
Subject: macro invocations with no arguments


Consider the code:

   #define m0()  replacement
    #define m1(x) begin x end
    m0() m1()

The number of arguments in a macro invocation is defined by 6.10.3#11:

[#11] The sequence of preprocessing tokens bounded by the outside-most matching parentheses forms the list of arguments for the function-like macro. The individual arguments within the list are separated by comma preprocessing tokens, but comma preprocessing tokens between matching inner parentheses do not separate arguments.

while 6.10.3#4 reads:

[#4] If the identifier-list in the macro definition does not end with an ellipsis, the number of arguments (including those arguments consisting of no preprocessing tokens) in an invocation of a function-like macro shall equal the number of parameters in the macro definition. Otherwise, there shall be more arguments in the invocation than there are parameters in the macro definition (excluding the ...). There shall exist a ) preprocessing token that terminates the invocation.


EITHER: the invocation of m0 has a single argument,
OR: the invocation of m1 has no arguments,

and in either case the requirement of 6.10.3#4 is violated.

This is clearly not the intent.

Suggested Technical Corrigendum

Append to 6.10.3#4:

If the invocation has no preprocessing tokens between the parentheses, this shall count as one argument unless the macro definition has neither an identifier list nor an ellipsis, in which case it shall count as no arguments.

Committee Response

The standard is clear enough, and no change is needed.

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