Attempt to access private member in dynamic_bitset - boost

Question

I am using Visual Studio 2017 to build LucenePlusPlus which in turn uses boost/dynamic_bitset.
The following code in LucenePlusPlus
const uint64_t* BitSet::getBits() {
return bitSet.empty() ? NULL : static_cast<const uint64_t*>(&bitSet.m_bits[0]);
}
generates the following fatal compiler error:
1>g:\luceneplusplus\src\core\util\bitset.cpp(20): error C2248: 'boost::dynamic_bitset<uint64_t,std::allocator<Block>>::m_bits': cannot access private member declared in class 'boost::dynamic_bitset<uint64_t,std::allocator<Block>>'
1> with
1> [
1> Block=uint64_t
1> ]
Suggestions?

Answer 1

I have traced the code for my boost 1_75_0 and I see it has a define to conditionally reserve access to friends:
#if defined(BOOST_DYNAMIC_BITSET_DONT_USE_FRIENDS)
#define BOOST_DYNAMIC_BITSET_PRIVATE public
#else
#define BOOST_DYNAMIC_BITSET_PRIVATE private
#endif
So it looks like you should be able to add -DBOOST_DYNAMIC_BITSET_DONT_USE_FRIENDS to the compiler defines to fix this.
In fact, my LucenePlusPlus tree already contains it in
include/config_h/Config.h.in line 107:
#define BOOST_DYNAMIC_BITSET_DONT_USE_FRIENDS
Previously ("rebuilt cmake buildsystem") this apparently
came from include/Config.h.cmake, where it was always present, unconditionally all the way since 2010:
What Can You Do?
Maybe you are not including the required headers that include the config? Also check any interfering precompiled header settings.
If you have boost/dynamic_bitset.hpp included BEFORE including LucenePlusPlus headers at any point you will run with the wrong config.
This is especially bad if you don't detect it because that would violate the ODR rule