Maintaining Directory Hierarchies with the Recursive Makefiles

If you extend your project hierarchy to include more layers, chances are that not only will the makefile in each intermediate directory have to produce target files, but it will also have to invoke nested make commands for subdirectories of its own.

Files in the current directory can sometimes depend on files in subdirectories, and their target entries need to depend on their counterparts in the subdirectories.

The nested make command for each subdirectory should run before the command in the local directory. One way to ensure that the commands run in the proper order is to make a separate entry for the nested part and another for the local part. If you add these new targets to the dependency list for the original target, its action will encompass them both.