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Modularity in C

Modularity in C. Giovanni Squillero Politecnico di Torino - DAUIN giovanni.squillero@polito.it. Scope. An identifier is visible (i.e., it can be used) only within a region of program text called its scope Four kinds of scopes function file block function prototype. . Scope.

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Modularity in C

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  1. Modularity in C Giovanni SquilleroPolitecnico di Torino - DAUINgiovanni.squillero@polito.it

  2. Scope • An identifier is visible (i.e., it can be used) only within a region of program text called its scope • Four kinds of scopes • function • file • block • function prototype. Advanced Programming

  3. Scope • An identifier is visible (i.e., it can be used) only within a region of program text called its scope • Four kinds of scopes • function • file • block • function prototype only labels! within a prototype Advanced Programming

  4. Scope: Example #include <stdio.h> int Glob; int myFunction(int parameter){ int lcl1; … } int myFunction2(int parameter){ int lcl2; … } Advanced Programming

  5. Scope: Example FILE #include <stdio.h> int Glob; int myFunction(int parameter){ int lcl1; … } int myFunction2(int parameter){ int lcl2; … } Advanced Programming

  6. Scope: Example BLOCK #include <stdio.h> int Glob; int myFunction(int parameter){ int lcl1; … } int myFunction2(int parameter){ int lcl2; … } Advanced Programming

  7. Storage duration • An object has a storage duration that determines its lifetime. • There are three storage durations: • static • automatic • allocated Advanced Programming

  8. Storage duration • An object has a storage duration that determines its lifetime. • There are three storage durations: • static • automatic • allocated Next lesson Advanced Programming

  9. Initialization • All objects with static storage duration are initialized (set to their initial values) before program startup • Automatic objects are not initialized by default Advanced Programming

  10. Storage classes specifiers • typedef • extern • static • auto • register Advanced Programming

  11. Storage classes specifier “syntactic convenience only” • typedef • extern • static • auto • register Advanced Programming

  12. Storage classes specifier AUTOMATIC STORAGEDURATION • typedef • extern • static • auto • register Advanced Programming

  13. Storage classes specifier STATIC STORAGEDURATION • typedef • extern • static • auto • register Advanced Programming

  14. Linkages of identifiers • External linkage • Internal linkage • No linkage Advanced Programming

  15. Linkages of identifiers ID2 EXTERNAL ID1 ID1 INTERNAL ID2 LINKER Advanced Programming

  16. Linkages: Example #include <stdio.h> int Glob;static int _Private; int myFunction(int parameter){ int lcl; extern ref; … return 0;} Advanced Programming

  17. Linkages: Example NO LINKAGE #include <stdio.h> int Glob;static int _Private; int myFunction(int parameter){ int lcl; extern ref; … return 0;} Advanced Programming

  18. Linkages: Example INTERNAL #include <stdio.h> int Glob;static int _Private; int myFunction(int parameter){ int lcl; extern ref; … return 0;} Advanced Programming

  19. Linkages: Example EXTERNAL #include <stdio.h> int Glob;static int _Private; int myFunction(int parameter){ int lcl; extern ref; … return 0;} Advanced Programming

  20. Summary • Scope • Where an identifier can be used • Storage • When an object can be used • Linkage • When an object can be used Advanced Programming

  21. What about functions? • Function identifiers • Always file scope • Always static storage duration • Either external (default) or internal (static functions) linkage Advanced Programming

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