Module Systems: Information Hiding Symbols and types Multiple implementations Type Safe Linking Separate compilation Modules in C? Physical modules: .c files as implementations; .h as interfaces Documented? - No. Practiced? - Yes

1. Designing a Module and Type Safe Linking For C For Documentation and Downloads Visit

4. Violating Modularity Properties CMod bitmap.h: struct BM; void init( struct BM *); void set( struct BM *, int ); bitmap.c: struct BM { int data; }; void set( struct BM *map, int bit) { … } void privatefn( void ) { … } Provider Client main.c: #include “bitmap.h” int main( void ) { struct BM *bitmap; init ( bitmap ); set ( bitmap , 1 ); … } int main( void ) { struct BM *bitmap; init ( bitmap ); set ( bitmap , 1 ); … } void init( struct BM *map , int val ) { … } extern void privatefn( void ); privatefn(); struct BM { int *data; }; bitmap .data = … #include “bitmap.h” void init( struct BM *map) { … } Interface--Implementation disconnect Violating Type Abstraction Accessing Private Functions Bottom-line: Compiler happy, but information hiding type-safe linking not guaranteed

6. CMod symbols type Rule 1: Shared Headers Rule 2: Type Ownership preprocessor interaction ???

7. Preprocessor configuration CMod Provider switches between two versions of the implementation depending on the flag COMPACT The order of these includes is important Its important that both files be compiled with the same -D flags

15. Queries FindBugs For Documentation and Downloads Visit