.. _ALLOW_CXXFLAGS_OVERWRITE:

ALLOW_CXXFLAGS_OVERWRITE
========================

.. cmake_variable:: ALLOW_CXXFLAGS_OVERWRITE

   Setting this option will allow you to overload preprocessor definitions from
   the command line, as it was possible naturally with the autotools build system.
   This feature only works with a :code:`Unix Makefiles` based generator. You can
   use it as:

   :code:`make CXXFLAGS="your flags" GRIDTYPE="grid type"`

   :code:`GRIDTYPE` can be anything defined in :code:`config.h` via the :ref:`dune_define_gridtype` macro from dune-grid.
   Furthermore any CPP variable of the form :code:`-DVAR=VALUE` can be overloaded on the command line.

   .. note::
      If you don't know what this is or what it's good for, don't use it.

