Eigen included before LehrFEM++

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You are here because you encountered the following warning during compilation:

warning: "Eigen has been included before LehrFEM++ and LF_REDIRECT_ASSERTS=On in cmake. Not all Eigen Asserts may print a stacktrace!" [-W#warnings]

What's the problem

LehrFEM++ normally tries to give you a stacktrace when an eigen_assert is failing. For this LehrFEM++ must redefine the eigen_assert macro so that it calls a LehrFEM's LF_ASSERT_MSG() macro.

This works only, if you include LehrFEM++ headers before any eigen headers.

Otherwise, you may get get the warning from above.

How to fix it

You have three options:

1. Fix the include order and make sure LehrFEM++ is included before Eigen.
2. Tell LehrFEM++ to not override the eigen_assert macro. You will not get a stacktrace when an eigen assert fails.
3. Ignore the warning.

1. Fix the include order

When the warning is emitted by the compiler, it will usually also tell you how lf_assert.h has been included. An Example Error message produced by clang:

In file included from /home/raffael/lehrfempp/lib/lf/io/gmsh_file_v4_binary.cc:11:
In file included from /home/raffael/lehrfempp/lib/lf/io/gmsh_file_v4_detail.h:42:
In file included from /home/raffael/lehrfempp/lib/lf/io/gmsh_file_v4.h:13:
In file included from /home/raffael/lehrfempp/lib/lf/mesh/mesh.h:22:
In file included from /home/raffael/lehrfempp/lib/lf/mesh/entity.h:4:
In file included from /home/raffael/lehrfempp/lib/lf/base/base.h:48:
In file included from /home/raffael/lehrfempp/lib/lf/base/eigen_tools.h:12:
/home/raffael/lehrfempp/lib/lf/base/lf_assert.h:82:2: warning: "Eigen has been included before LehrFEM++ and LF_REDIRECT_ASSERTS=On in cmake. Not all Eigen Asserts may print a stacktrace!" [-W#warnings]
#warning \
 ^

You can then follow the include hierarchy from the beginning (gmsh_file_v4_binary.cc) until you reach lf_assert.h. At every step you should check if any Eigen header is #included before a LehrFEM++ header.

2. Tell LehrFEM++ to not override the eigen_assert macro

LehrFEM++ has the cmake option LF_REDIRECT_ASSERTS which is by default enabled. You can disable this option and thereby tell LehrFEM++ to not redirect eigen and boost asserts to LF_ASSERT_MSG.

2.1. If you compile LehrFEM++ directly

You can just issue the following command in your cmake build directory:

cmake -D LF_REDIRECT_ASSERTS=Off .

2.2. If you use LehrFEM++ via hunter

1. Create the file cmake/Hunter/config.cmake in your repository.
2. Put the following command into it:

   hunter_config(lehrfempp CMAKE_ARGS LF_REDIRECT_ASSERTS=Off)

3. modify the HunterGate command in your top-level CMakeLists.txt as follows:

   HunterGate(
    URL do_not_change
    SHA1 do_not_change
    LOCAL # use cmake/Hunter/config.cmake
   )