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

From: Wu Yinghui, Freddie (yhwu_at_[hidden])
Date: 2006-03-08 08:44:38

 > What is going wrong?  I tried it on VC7, VC7.1, and VC8, and it
appeared to work correctly on all three versions of the compiler.

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

 > I've seen strange problems related to __LINE__ on VC before, but I
 > can't remember off the top of my head what the issue was.
 > (Thinking...)  It has something to do with the generation of debug
 > information.  Okay, yes, I see the error that you are getting now.  It
 > only happens in during a debug build.

You are right. It occurs only in debug builds. (Sorry for forgetting to
mention this.)

 > This is just one of the *many* ways in which VC's preprocessor is
 > wacky.  It suffices to say it isn't even in the ballpark of
 > implementing the phases of translation correctly.

That's what I feel. The error message indicate that the compiler somehow
considers "id" and __LINE__ two identifier when the error occurs. I
tried using the /P parameter to dump the preprocessed source, and that
looked fine, though. So I guess it is the problem with MSVC compiler
mixing preprocessing and parsing phases together...

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

 > What do you mean by "certain scope"?  Or, more precisely, given a
 > finite scope such as that defined by a function, why do you need
 > unique identifiers?  Most of the time when people want unique
 > identifiers, they want an identifier that is unique across an entire
 > program or, at minimum, inside a translation unit.

Well... The scope can be the whole program, or in a namespace, or in a
translation unit. The unique ID is used in a macro in the library for
some tidious code that can be automatically generated using preprocessor.

Anyway, thanks for Stewart Tootill's suggestion. I had to resort to
using __COUNTER__ at the meantime, which seemed working so far. (But one
thing that worries me is that __COUNTER__ is only unique within a
translation unit. So what if I need a unique identifier throughout the
program?)

 > Regards,
 > Paul Mensonides

Thanks for your comments.

Cheers,

Freddie