Use a portable way to get the relative paths into __FILENAME__

CMakeLists.txt

@@ -11,10 +11,6 @@ if("${CMAKE_CXX_COMPILER_ID}" STREQUAL "GNU")
   set(CMAKE_CXX_FLAGS_DEBUG "${CMAKE_CXX_FLAGS_DEBUG} -fprofile-arcs -ftest-coverage --coverage")
 endif()
 
-# Define a __FILENAME__ macro to get the filename of each file, instead of
-# the full path as in __FILE__
-set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -D__FILENAME__='\"$(subst ${CMAKE_SOURCE_DIR}/,,$(abspath $<))\"'")
-
 #
 ## Look for external libraries
 #
@@ -207,6 +203,14 @@ if(USE_DATABASE)
   database)
 endif()
 
+# Define a __FILENAME__ macro with the relative path (from the base project directory)
+# of each source file
+file(GLOB_RECURSE source_all src/*.[hc]pp tests/*.[hc]pp)
+foreach(file ${source_all})
+  file(RELATIVE_PATH shorter_file ${CMAKE_CURRENT_SOURCE_DIR} ${file})
+  set_property(SOURCE ${file} APPEND PROPERTY COMPILE_DEFINITIONS __FILENAME__="${shorter_file}")
+endforeach()
+
 include(ExternalProject)
 ExternalProject_Add(catch
   GIT_REPOSITORY "https://lab.louiz.org/louiz/Catch.git"