C++ projects have headers in different directories than sources. Thus you need to specify include directories. Let's assume that we are at some subdirectory and wish to add its
include subdirectory to some target's search path. To create a include directory object we do this:
incdir = include_directories('include')
incdir variable now holds a reference to the
include subdir. Now we pass that as an argument to a build target:
executable('someprog', 'someprog.c', include_directories : incdir)
Note that these two commands can be given in any subdirectories and it will still work. Meson will keep track of the locations and generate proper compiler flags to make it all work.
Another thing to note is that
include_directories adds both the source directory and corresponding build directory to include path, so you don't have to care.
The results of the search are