Namespaces, Typedefs & Enums

Tricks for naming things

Name Collisions

• Including lots of libraries…– Library A defines:bool checkPositive(int x);

– Library B defines:bool checkPositive(int y);

Name Spaces

• Namespaces break names into groups

• To use something from namespace, specify namespace to resolve it in:LibA::checkPositive(10);

LibA::checkPositive(int x)LibA::somethingElse()LibA::x

LibB::checkPositive(int x)LibB::otherThing()

Declaring in Namespace

• Can invent any arbitrarynamespace like this

Using

• Using can bring in…– Whole namespace

– One identifier

Let me use anything fromLibrary1 without Library1::

Let me use foo() fromLibrary1 without Library1::

Not Using Using

• Putting using namespace std in .h file frowned upon • std:: has lots of names• Anyone including your .h now stuck with them

Typedef

• typedef creates a new name for existing type– Does not create new types!

typedef exitingType newName;

• Ex:typedef int number;

number x = 10; //number really means int

Why Typedef

• Bad uses– Renaming int to number

Why Typedef

• Good uses– Ugly constructs:

std::vector<std:pair<int, int> >::iterator myIt;

std::vector<std:pair<int, int> >::iterator myOtherIt;

Vs:typedef std::vector<std:pair<int, int> >::iterator VectorPairIterator;

VectorPairIterator myIt;

VectorPairIterator myOtherIt;

Why Typedef

• Good uses– Dealing with platform issues

//On PC:typedef int int32;//On arduino processortypedef long int32;

//anywhere:

int32 myNum; //int32 definitely has 32 bits

Constant Issue

• Constants = readable code

Constant Issue

• Don't protect us from stupidity:

Enums

• Enumerated Type – Custom data type with discrete set of possible

values

A weekday is something from:{Monday, Tuesday, Wednesday, Thursday, Friday}

Enums

• Syntax: enum newType {valueList};

• Sample enums:enum standing {FRESHMAN, SOPHOMORE,

JUNIOR, SENIOR};

enum color {RED, BLUE, GREEN, BLACK, ORANGE};

Enum Use

• Enum usage– Can make variables of that type– Variables can only have given values

enum standing {FRESHMAN, SOPHOMORE, JUNIOR, SENIOR};

standing studentYear = FRESHMAN;

standing student2Year = 12; //Error

Enums

• Pluses of constants, without dangers

Enum Rules

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

Enum Rules

• Enum values must be valid identifiers• Can't reuse identifiers

Enum Rules

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

Enum Values

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

Enum Values

• Enums stored as integral values– Can modify by assigning

{Monday, Tuesday, Wednesday, Thursday, Friday} 10 11 30 31 32

Enum Values

• Only use assignment/value if represent logical value:

Relational Operators

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

Interacting:

• Cin can't read into enum type

– Read in string/int, use if:

Interacting:

• Cout will print as number

– Print using if/switch/array

Interacting:

• Legal to switch based on enum:

Enum’s & Math

• Math with enum results in an int

Enum’s & Math

• Can static cast into an enum– Can go out of range!

Enum’s & Math

• Can static cast into an enum– Can go out of range!

– Prevent:

Enum’s & Math

• Looping with enum:

Enum’s & Math

• Work normally as parameteror return type: