[Boost-users] [TR1] Configuration macros

From: Scott Meyers (usenet_at_[hidden])
Date: 2007-05-30 19:16:23

I'm having trouble understanding the information at 
http://www.boost.org/doc/html/boost_tr1/config.html, and having already spent a 
fair amount of time running test programs and pouring over the output of the 
preprocessor for various compilers, I'm hoping that somebody in the know can 
just explain things to me.

My goal is simple:  use Boost.TR1 such that if my compiler ships with a library 
with support for whatever TR1 component I want to use, I'll get that native 
support.  But if the library that ships with the compiler lacks support for the 
TR1 component I need, I want to fall back on the Boost implementation, if there 
is one.  And I want to uniformly refer to TR1 components as if they are in the 
namespace std::tr1.

My reading of the above-referenced page leads me to believe that this is the 
behavior I'm supposed to get by default.  And it's consistent with the tests 
I've performed using VC8 and g++ 4.1.  But then I read this:

> The configuration macros used by each TR1 component are documented in each library section (and all together in the Boost.Config  documentation), but defining BOOST_HAS_TR1 will turn on native TR1 support for everything (if your standard library has it), which can act as a convenient shortcut.

This kind of suggests that I should define BOOST_HAS_TR1.  Should I?  So far I 
have not.

And then I read this:

> Boost.TR1 does not currently enable gcc's native TR1 implementation as this is currently in an early stage of development. However, you may choose to do so by defining BOOST_HAS_GCC_TR1.

This pretty clearly suggests that I should define BOOST_HAS_GCC_TR1.  Should I? 
  So far, I have.  I've also found that unless I define it like this,

> #ifdef __GNUC__
> #define BOOST_HAS_GCC_TR1
> #endif

compilation with VC8 fails, which I find kind of strange.  Here's an error I get:

> D:\C++\Boost\Current\boost/tr1/type_traits.hpp(11): fatal error C1083: Cannot open include file: 'type_traits': No such file or dire
> ctory

Why should defining BOOST_HAS_GCC_TR1 have any effect on a VC8 compilation?

All clarification about the correct settings of TR1 configuration macros for at 
least VC8 and g++ 4.1 would be much appreciated.

Thanks,

Scott