Namespaces, Typedefs & Enums

1. Namespaces, Typedefs & Enums Tricks for naming things

2. Name Collisions • Including lots of libraries… • Library A defines:bool checkPositive(int x); • Library B defines:bool checkPositive(int y);

3. Name Spaces • Namespaces break names into groups • To use something from namespace, specify namespace to resolve it in:LibA::checkPositive(10); LibB::checkPositive(int x) LibB::otherThing() LibA::checkPositive(int x) LibA::somethingElse() LibA::x

4. Declaring in Namespace • Can invent any arbitrarynamespace like this 

5. Using • Using can bring in… • Whole namespace • One identifier Let me use anything fromLibrary1 without Library1:: Let me use foo() fromLibrary1 without Library1::

6. Not Using Using • Best practice : don't include whole std namespace in .h files • std:: has lots of names • Anyone including your .h now stuck with them

7. Typedef • typedefcreates a new name for existing type • Does not create new types! typedef exitingType newName; • Ex: typedefintnumber; number x = 10; //number really means int

8. Why Typedef • Bad uses • Renaming int to number

9. Why Typedef • Good uses • Ugly constructs: std::vector<std:pair<int, int> >::iterator myIt; std::vector<std:pair<int, int> >::iterator myOtherIt; Vs: typedefstd::vector<std:pair<int, int> >::iterator VectorPairIterator; VectorPairIterator myIt; VectorPairIteratormyOtherIt;

10. Why Typedef • Good uses • Dealing with platform issues //On PC:typedefintint32;//On arduino processortypedeflong int32; //anywhere: int32 myNum; //int32 definitely has 32 bits

11. Constant Issue • Constants = readable code

12. Constant Issue • Don't protect us from stupidity:

13. Enums • Enumerated Type • Custom data type with discrete set of possible values A weekday is something from:{Monday, Tuesday, Wednesday, Thursday, Friday}

14. Enums • Syntax: enum newType {valueList}; • Sample enums: enum standing {FRESHMAN, SOPHOMORE, JUNIOR, SENIOR}; enum color {RED, BLUE, GREEN, BLACK, ORANGE};

15. Enum Use • Enumusage • Can make variables of that type • Variables can only have given values enum standing{FRESHMAN, SOPHOMORE, JUNIOR, SENIOR}; standingstudentYear = FRESHMAN; standing student2Year = 12; //Error

16. Enums • Pluses of constants, without dangers

17. Enum Rules • Enum values must be valid identifiers • Start with letter, no special symbols, etc…

18. Enum Rules • Enum values must be valid identifiers • Can't reuse identifiers

19. Enum Rules • Enum values must be valid identifiers • Can't reuse values • Enum type names should be singular • Don't want:grades JohnsGrade;

20. Enum Values • Enums stored as integral values • Starting from 0: {Monday, Tuesday, Wednesday, Thursday, Friday} 0 1 2 3 4

21. Enum Values • Enums stored as integral values • Can modify by assigning {Monday, Tuesday, Wednesday, Thursday, Friday} 10 1130 3132

22. Enum Values • Only use assignment/value if represent logical value:

23. Relational Operators • Relational operations work based on assigned values (order of enumerated values)

24. Interacting: • Cin can't read into enum type • Read in string/int, use if:

25. Interacting: • Cout will print as number • Print using if/switch/array

26. Interacting: • Legal to switch based on enum:

27. Enum’s & Math • Math with enum results in an int

28. Enum’s & Math • Can static cast into an enum • Can go out of range!

29. Enum’s & Math • Can static cast into an enum • Can go out of range! • Prevent:

30. Enum’s & Math • Looping with enum:

31. Enum’s & Math • Work normally as parameteror return type: