preprocessor/10513: Annoying warning

preprocessor/10513: Annoying warning

[csimon]

>Number:         10513
>Category:       preprocessor
>Synopsis:       Annoying warning
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    unassigned
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sun Apr 27 14:46:01 UTC 2003
>Closed-Date:
>Last-Modified:
>Originator:     SIMON Claude
>Release:        gcc version 3.2 20020927 (prerelease)
>Organization:
>Environment:
Cygwin or GNU/Linux
>Description:
When compiling the below source file ('g++ dummy.cpp'), I obtain this message :

---
dummy.cpp:9:14: warning: pasting "::" and "i" does not give a valid preprocessing token
---

This happend with all gcc 3.x releases. It doesn't happend with the gcc releases prior to 3.x, and other compilers (Borland C++, Visual C++, Metrowerks CodeWarrior) don't issue this warning.
I'm not really sure if this is a bug, but, if not, can you say me what's wrong ?
Thanks !

--- Begin of dummy.cpp source file ---
namespace n {
	int i;
}

#define M(a)	a##i

int main( void )
{
	M(n::) = 42;	// The line which produces the preprocessor warning.

	return 0;
}
--- End of dummy.cpp source file ---
>How-To-Repeat:
g++ dummy.cpp
>Fix:

>Release-Note:
>Audit-Trail:
>Unformatted:

Re: preprocessor/10513: Annoying warning

[nathan]

Synopsis: Annoying warning

State-Changed-From-To: open->closed
State-Changed-By: nathan
State-Changed-When: Sun Apr 27 15:11:32 2003
State-Changed-Why:
    not a bug. the result of ## is undefined if it does not result
    in a pp token. '::i' is not a pp token.
    #define M(a) a i // this is fine

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=10513