Adding include directories to CMake when calling it from the command line

I have the same problem. I found two solutions:

1. The one proposed by sakra in a previous answer, i.e. setting an environment variable with C++ flags:

   export CXXFLAGS=-isystem\ /path/to/my/include
   cmake <path to my sources>
   

   OR the same thing, but environment variable are set only for this CMake call:

   CXXFLAGS=-isystem\ /path/to/my/include cmake <path to my sources>
   

   IMPORTANT: you must clean your build directory (i.e. clean the CMake cache) before launching any of this form. Without cleaning the cache, CMake will continue using your cached CMAKE_CXX_FLAGS from the previous run.

2. Directly setting CMAKE_CXX_FLAGS in cmake string:

   cmake -DCMAKE_CXX_FLAGS=-isystem\ /path/to/my/include <path to my sources>
   

I believe that it can be done by a more 'native' way, but I didn't find a variable responsible for paths to headers in CMake.

You can set the environment variable CXXFLAGS before invoking CMake.

$ export CXXFLAGS=-isystem\ /path/to/my/include
$ cmake ..

CMake will the initialize the cache variable CMAKE_CXX_FLAGS with the flags from the environment variable. The variable affects all build types.