[cfe-dev] Best way to detect libc++ at compile time?

[Howard Hinnant]

On Jul 19, 2012, at 10:19 PM, Rich E <reakinator at gmail.com> wrote:

> Hi all,
> 
> I am enabling libc++ in a library that was depending on boost for things such as mutex, thread, shared_ptr, etc., and I have not yet found a way to detect that we are compiling with the libc++ library unless I first include a header from it.  I can do this:
> 
> // framework config.h:
> 
> #include <vector>
> 
> #if defined( _LIBCPP_VERSION )
>     #define USING_LIBCPP
> #endif
> 
> but now every file that wanted to know if we are using libc++ has vector in it. This include is used to determine which standard library we should use, and many things depend on it. Is there a better solution, other than a -D flag to clang?

My solution is very similar to yours except I use <ciso646>.  The C++ specification specifically says that #include <ciso646> has no effect.  So it is very cheap to include.

The libc++ implementation of <ciso646> is:

#ifndef _LIBCPP_CISO646
#define _LIBCPP_CISO646

#include <__config>

#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
#pragma GCC system_header
#endif

#endif  // _LIBCPP_CISO646

And <__config> will #define _LIBCPP_VERSION.  All libc++ headers include <__config> as the first thing.  Other implementations of <ciso646> will not (I hope) #define _LIBCPP_VERSION.

Howard