The Fl_Tree project can either be added to FLTK, or installed as a subdirectory either inside your own project, or in a separate directory that all your projects can refer to.
Just be sure to compile with the -I (include) flag pointing to where the Fl_Tree directory is, and link in "Fl_tree.a" left in the Fl_Tree main directory after doing a 'make'.
Installing Fl_Tree Into Your Project's DirectoryHere's an example of how to install Fl_Tree into your project's own directory:../src/YourApp/ | |-- YourApp.C |-- YourApp.H -- Contains "#include <FL/Fl_Tree.H>" |-- Makefile -- Compiles with "-I./Fl_Tree", links with ./Fl_Tree/Fl_Tree.o |-- Fl_Tree -- Fl_Tree installed as a subdirectory : | |-- FL -- Fl_Tree include files | | | |-- Fl_Tree.H -- include this in your code with #include <FL/Fl_Tree.H> | : | |-- Fl_Tree.a -- The Fl_Tree library | |-- Makefile -- Fl_Tree Makefile :This way you can still just have "#include <FL/Fl_Tree.H>" in your C++ files. Just use "-I./Fl_Tree" as one of the compile flags, and the #include will resolve correctly.
During linking, be sure to link in Fl_Tree.a file as part of the link instructions for your app.