C++11 non-conforming __VA_ARGS__ macro expansion (C4003)

C++11 non-conforming __VA_ARGS__ macro expansion (C4003) by Igor 'arabesc' Pavlov

Closed

as Deferred Help for as Deferred

Type:	Bug
ID:	772051
Opened:	11/23/2012 6:30:33 AM
Access Restriction:	Public

Workaround(s)

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User(s) can reproduce this bug

Microsoft Visual Studio Ultimate 2012
Version 11.0.51020.03 Update 1 CTP

Visual C++ 2012 04940-004-0038003-02800
Microsoft Visual C++ 2012

Visual C++ Compiler November 2012 CTP [Codename Milan] installed.

There is nonstandard __VA_ARGS__ expansion.

C++11 draft:
16.3.1 Argument substitution
1. After the arguments for the invocation of a function-like macro have been identified, argument substitution takes place. A parameter in the replacement list, unless preceded by a # or ## preprocessing token or followed by a ## preprocessing token (see below), is replaced by the corresponding argument after all macros contained therein have been expanded. Before being substituted, each argument’s preprocessing tokens are completely macro replaced as if they formed the rest of the preprocessing file; no other preprocessing tokens are available.
2. An identifier __VA_ARGS__ that occurs in the replacement list shall be treated as if it were a parameter, and the variable arguments shall form the preprocessing tokens used to replace it.

Details (expand)

Visual Studio 2012

Compile it:

#include <iostream>

#define PP_TEST(...) PP_TEST2(__VA_ARGS__)
#define PP_TEST2(a, b) #a

int main()
{
std::cout << PP_TEST(0, 1) << std::endl;
}

English

Windows 8

Any

Compiler output:
warning C4003: not enough actual parameters for macro 'PP_TEST2'

Program output:
0, 1

Right macro expansion, no compiler warning.
Program output:
0

0 attachments

Posted by Microsoft on 11/25/2012 at 11:13 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 11/23/2012 at 6:52 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 Igor 'arabesc' Pavlov on 11/23/2012 at 6:32 AM

#include <iostream>

#define PP_SUBST(arg) arg
#define PP_TEST(...) PP_SUBST(PP_TEST2(__VA_ARGS__))
#define PP_TEST2(a, b) #a

int main()
{
std::cout << PP_TEST(0, 1) << std::endl;
}