"Forwarded" __VA_ARGS__ can't be split up? by demett

Closed

as Deferred Help for as Deferred

Type:	Bug
ID:	778757
Opened:	2/7/2013 10:11:12 AM
Access Restriction:	Public

Workaround(s)

view

User(s) can reproduce this bug

This:

#define WORKS(X, Z, ...) (Z, X, __VA_ARGS__)
#define DOESNT(X, ...) WORKS(X, __VA_ARGS__)
WORKS(1, 2, 3, 4, 5)
DOESNT(1, 2, 3, 4, 5)

preprocesses to:

(2, 1, 3, 4, 5)
(2, 3, 4, 5, 1 )

The DOESNT macro should expand to the same thing as the WORKS macro, but it doesn't. It looks like the preprocessor is avoiding splitting up the forwarded __VA_ARGS__.

Details (expand)

Visual Studio 2012

cat >test.c
#define WORKS(X, Z, ...) (Z, X, __VA_ARGS__)
#define DOESNT(X, ...) WORKS(X, __VA_ARGS__)
WORKS(1, 2, 3, 4, 5)
DOESNT(1, 2, 3, 4, 5)

cl /EP test.c

English

Windows 7

English

(2, 1, 3, 4, 5)
(2, 3, 4, 5, 1 )

(2, 1, 3, 4, 5)
(2, 1, 3, 4, 5)

0 attachments

Posted by Microsoft on 2/7/2013 at 6:38 PM

Thanks for your feedback.

We are rerouting this issue to the appropriate group within the Visual Studio Product Team for triage and resolution. These specialized experts will follow-up with your issue.

Posted by Microsoft on 2/7/2013 at 10:51 AM

Thank you for your feedback, we are currently reviewing the issue you have submitted. If this issue is urgent, please contact support directly(http://support.microsoft.com)

Posted by demett on 2/7/2013 at 10:12 AM

This particular case can be worked around by explicitly forwarding Z in the DOESNT macro:

#define WORKS(X, Z, ...) (Z, X, __VA_ARGS__)
#define DOESNT(X, Z, ...) WORKS(X, Z, __VA_ARGS__)
WORKS(1, 2, 3, 4, 5)
DOESNT(1, 2, 3, 4, 5) // Actually, it does now

Microsoft