CMOD : Enforcing Modularity in C Code

Many modern languages have sophisticated linguistic support for modular programming. In these languages, the different components of a system can be developed independently, and when combined together the resulting program will be type correct. The C programming language does not contain direct support for modules, but over time programmers have developed a discipline of modular programming which treats .c files as modules and .h header files included by C’s preprocessor cpp as interfaces. However, without proper enforcement, a mistake can easily lead to a confusing error and time wasted tracking it down. This paper presents CMOD, a tool that enforces rules to ensure that common idioms for modularity are used correctly, and thus the program is compiled correctly. CMOD easily fits within the development process as a front-end for the compiler and linker (e.g., gcc and ld). We have tested CMOD on a number of open source software systems and found that each exhibits a small number of violations of our rules, all of which can be easily fixed.