Incl: A Tool to Analyze Include Files

Large C and C++ software projects typically share common types, macros, and variables among modules via include files organized into hierarchies. Many of these hierarchies grow so complex that it is hard for programmers to figure out when a file must be included. Since including unused symbols is usually harmless, application code tends to include more files than required. Knowing when files are or are not needed is useful to restructure the code and reduce the time required to build a product. It also helps in reorganizing the include hierarchies - should this be deemed necessary. Incl is a tool that analyzes include hierarchies to (1) show the dependencies among include files in graphical or text forms, (2) infer what files are not needed, and (3) provide ways to remove unused include files. The inference and removal of unused include files must be done with care for that may change the meaning of the application programs. We shall describe precise conditions under which include files can be safely ignored for compilation and give a linear time algorithm to compute such files. Incl has been used on many projects and experience shows that, in many cases, eliminating unnecessary include files significantly reduces compilation time.