Re: [eigen] Eigen 3.3.0 compile error with aligned_allocator

[Gael Guennebaud <gael.guennebaud@xxxxxxxxx>]

Hi,

sorry for late reply, but I cannot reproduce. I tried clang, gcc, and MSVC 19.00 (boost 1.59 and 1.60).

See this self-contained example:

http://rextester.com/XHGN60496

BTW, I don't see how the reported error is related to operator==. Moreover, I think that the error message is incomplete, please paste the complete error message so that we can see what the template instantiations that led to this error.

gael

On Wed, Nov 16, 2016 at 8:38 AM, Lodron, Gerald <Gerald.Lodron@xxxxxxxxxxx> wrote:

Hi

I am compiling PCL trunk with Eigen3.3.0 (and VS2013x64, boost 1.62.0) and get a compilation error on the intantiation of
…
typedef boost::unordered_map<int, Leaf, boost::hash<int>, std::equal_to<int>, Eigen::aligned_allocator<int> > HashMap;
…
HashMap cell_hash_map_;


E:\Develop\Libraries120_x64\boost\1.62.0-NoPython\include\boost-1_62\boost/unordered/detail/allocate.hpp(497) : error C2664: 'Eigen::aligned_allocator<U>::aligned_allocator(const Eigen::aligned_allocator<U> &)' : cannot convert argument 1 from 'std::allocator<T>' to 'const Eigen::aligned_allocator<U> &'
        with
        [
            U=boost::unordered::detail::ptr_node<std::pair<const int,pcl::GridProjection<pcl::PointNormal>::Leaf>>
        ]
        and
        [
            T=boost::unordered::detail::ptr_node<std::pair<const int,pcl::GridProjection<pcl::PointNormal>::Leaf>>
        ]
        and
        [
            U=boost::unordered::detail::ptr_node<std::pair<const int,pcl::GridProjection<pcl::PointNormal>::Leaf>>
        ]
        Reason: cannot convert from 'std::allocator<T>' to 'const Eigen::aligned_allocator<U>'


I googled a little bit and found
http://stackoverflow.com/questions/16126133/compiling-issue-with-custom-allocators-when-std-c0x-is-enabled

“The error message actually contains the hint. I’ve reformulated it slightly here:
error: invalid operands [of type aligned_allocator<int>] to binary _expression_ […] __x._M_get_Tp_allocator() == this->_M_get_Tp_allocator()
In other words, your allocator type needs to provide an operator ==.
This is part of the allocator requirements (§17.6.3.5, table 28). This has always been the case. But until C++11 allocators were stateless and operator == consequently always returned true, so the standard library containers probably never called the operator. This would explain why the code compiles without -std=++0x.
“

Could it be that you need some operator definitions in the aligned_allocator of eigen? The compilation error is only since eigen 3.2.9, on eigen 3.2.8 it works. The difference which causes the error is the inheritance from std::allocator of Eigen::aligned_allocator....