Question

Summary:
I have a code snippet that compiles fine with g++ but not with clang.

Details:

I have a project that compiles fine with g++ but when compiling with clang I get an error about error: use of non-static data member. I tried to create a small test case that would demonstrate the problem, but for the small test case g++ gave the same error as clang.

I’ve posted a 236 line file to pastebin that demonstrates the problem:
http://pastebin.com/DGnfxmYe

When compiled with g++ 4.6.3 this works fine. But when compiled with clang 3.2 I get the following error messages:

myhashmap.hpp:169:29: error: use of non-static data member 'num_bins' of 'MyHashMap' from nested type 'iterator'
          for (_index++; (_index < num_bins) && (bins[_index] == NULL); _index++)
                                   ^~~~~~~~
myhashmap.hpp:169:43: error: use of non-static data member 'bins' of 'MyHashMap' from nested type 'iterator'
          for (_index++; (_index < num_bins) && (bins[_index] == NULL); _index++)
                                                 ^~~~
myhashmap.hpp:171:17: error: use of non-static data member 'num_bins' of 'MyHashMap' from nested type 'iterator'
          if (_index < num_bins) {
                       ^~~~~~~~
myhashmap.hpp:172:17: error: use of non-static data member 'bins' of 'MyHashMap' from nested type 'iterator'
            _theNode = bins[_index];
                       ^~~~

Looking at the code, it makes sense to me why clang is giving these error messages. What I don’t understand is why g++ compiled the code correctly in the first place. I did not write this code but I would like to get it to compile cleanly with clang. So I’m trying to understand exactly what it is doing. And I would be interested in understanding why it compiles with g++ but not with clang. Does g++ interpret the c++ standard differently, or is there some g++ extension that the code is taking advantage of?

Answer 1

It fails with GCC 4.8 (prerelease) so I assume it’s a bug that’s been fixed. I can’t find a corresponding bug report though.

To fix the code I think you’ll need add an int _num_bins member to the iterator and pass the cotnainer’s num_bins to the iterator constructor in begin() and end(), so it’s stored in each iterator object.

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(Additionally, don’t write (void) for a function taking no arguments, that’s an abomination. In C++ a function taking no arguments is written ())