C++ Boost Unordered_Set Compilation Error: 'Illegal Static Data Member'

If you are encountering an 'Illegal static data member' error when trying to compile C++ code that uses the boost::unordered_set class, it is likely because you are using an outdated version of the Boost library.

In older versions of Boost, the unordered_set class used a static data member called 'default_bucket_count' that caused this error when compiling with certain compilers.

To fix this issue, you can try one of the following solutions:

1. Upgrade to a newer version of the Boost library that does not have this issue. The latest version of Boost at the time of writing is 1.76.0.

2. If upgrading is not an option, you can try using the newer boost::unordered_set class, which has replaced the problematic 'default_bucket_count' static data member with a non-static member function called bucket_count(). This should resolve the compilation error.

Here's an example of how to use boost::unordered_set without encountering the 'Illegal static data member' error:

#include <boost/unordered_set.hpp>

int main() {
  boost::unordered_set<int> set;
  set.insert(1);
  set.insert(2);
  set.insert(3);

  for (const auto& element : set) {
    // Do something with each element
  }

  return 0;
}

Make sure to update your code accordingly and include the necessary Boost header files.