Re: [Boost-users] Boost.Preprocessor with __LINE__ in MSVC71

From: Stewart Tootill (stewart.tootill_at_[hidden])
Date: 2006-03-08 04:17:01

There is a known bug with MSVC71 where if you use __LINE__ too much (not sure what the limits are or under what circumstances though), you get a "Fatal Error: Out of Keys" or something similar. Instead of this, for generating unique variable names etc I have seen the __COUNTER__ macro used instead, which provides similar functionality, but doesn't seem to suffer from this issue.

Yours,

Stewart

-----Original Message-----
From: boost-users-bounces_at_[hidden]
[mailto:boost-users-bounces_at_[hidden]]On Behalf Of Wu Yinghui,
Freddie
Sent: 08 March 2006 09:00
To: boost-users_at_[hidden]
Subject: [Boost-users] Boost.Preprocessor with __LINE__ in MSVC71

Hi all,

I'm observing an interesting problem on MSVC71 regarding the use of 
__LINE__ with Boost.Preprocessor.

The code looks like this
==== snip ====
#include <boost/preprocessor/cat.hpp>
#define UNIQUE_ID   BOOST_PP_CAT(id, __LINE__)
#define UNIQUE_ID2   BOOST_PP_CAT(id, _MSC_VER)
int main()
{
     int UNIQUE_ID2 = 321;
     int UNIQUE_ID = 123;
     bool UNIQUE_ID = false;
}
==== snip ====

The compiler works fine with UNIQUE_ID2, but not UNIQUE_ID. The only 
different in them is only the use of __LINE__ instead of _MSC_VER.

Does anyone on the list has more insight on this issue?

Or, what're the common ways to generate an unique identifier 
automatically within certain scope?

Cheers,

Freddie

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Wu Yinghui, Freddie
Research & Development
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