Rules:
4.3.a. Each source file shall include only the behaviors appropriate to control one “entity”. Examples of entities include encapsulated data types, active objects, peripheral drivers (e.g., for a UART), and communication protocols or layers (e.g., ARP).
4.3.b. Each source file shall be comprised of some or all of the following sections, in the order listed: comment block; include statements; data type, constant, and macro definitions; static data declarations; private function prototypes; public function bodies; then private function bodies.
4.3.c. Each source file shall always #include the header file of the same name (e.g., file adc.c should #include “adc.h”), to allow the compiler to confirm that each public function and its prototype match.
4.3.d. Absolute paths shall not be used in include file names.
4.3.e. Each source file shall be free of unused include files.
4.3.f. No source file shall #include another source file.
Example: See Appendix D.
Reasoning: The purpose and internal layout of a source file module should be clear to all who maintain it. For example, the public functions are generally of most interest and thus appear ahead of the private functions they call. Of critical importance is that every function declaration be matched by the compiler against its prototype.
Enforcement: Most static analysis tools can be configured to check for include files that are not actually used. The other rules shall be enforced during code reviews.