1. CS212: Object Oriented Analysis and Design
Namespace

2. Introduction
Purpose is to localize the names of identifiers to avoid name collisions
Global namespace
Name defined by one library would conflict with the same name defined by the other library
Namespace allows the same name to be used in different contexts without conflicts arising
e.g. std

3. Namespace Fundamentals
Allows you to partition the global namespace
Creating a declarative region i.e. a namespace defines a scope
Inside a namespace, identifiers declared within that namespace can be referred to directly
Scope resolution operator to be used to refer to objects declared within a namespace from outside that namespace
Demonstration: namespace1.cpp

4. The ‘using’ keyword Use of :: always is a tedious task
The using statement was invented to alleviate this problem
The using statement has these two general forms
using namespace name;
using name::member;
using CounterNameSpace::lowerbound;
Demonstration: namespace2.cpp

5. Object Oriented Analysis and Design (CS 212)
Nested Namespace
Namespace defined within another namespace
Scope resolution operator to be used
Namespace1::Namespace2::member
Namespace1::member
Object Oriented Analysis and Design (CS 212)

6. Unnamed Namespaces
A special type of namespace, called an unnamed namespace
Allows to create identifiers that are unique within a file
To establish unique identifiers that are known only within the scope of a single file
Outside the file, the identifiers are unknown
Demonstration (file1 & file2.cpp)

7. Object Oriented Analysis and Design (CS 212)
Namespace Alias
Alias (alternate name) can be assigned to a namespace
Ease of programming
Similar to typedef
Object Oriented Analysis and Design (CS 212)

8. Object Oriented Analysis and Design (CS 212)
Koening Lookup
Argument-dependent lookup, also known as ADL, or Koenig lookup
Set of rules for looking up the unqualified function names 
function-call expressions, including implicit function calls to overloaded operators
These function names are looked up in
The namespaces of their arguments
The scopes and namespaces considered by the usual unqualified name lookup.
Object Oriented Analysis and Design (CS 212)

9. Advantage of Koening Lookup
myLine l1(point(2,5), point(9,10)); std::cout << “equation of line is: ”; std::cout << l1 << end;
Object Oriented Analysis and Design (CS 212)

10. In a nutshell Standard namespace Variables Functions Classes
User defined namespace
Variables
Functions
Classes
Variables
Functions
Classes

11. The std namespace
Standard C++ defines its entire library in its own namespace called std
using namespace std;
This causes the std namespace to be brought into the current namespace
Direct access to the names of the functions and classes defined within the library without using std::