1. Namespaces
How Shall I Name Thee?

2. Name Collision
by default, function, class, global constant and variable scope is global
in large programming projects multiple people may give different constructs the same name, resulting in name collision.
words like sort, find, count and print are tempting
name collision may result in
compile-time error - when header is included
linker error
namespaces – designed to sub-divide global scope and avoid name collision

3. Defining Namespaces
define a namespace block, declare constructs inside
namespace myNamespace{
const int limit=5;
void myFunc(int a){
++a; }
functions, classes, etc. (constructs with separate definitions) may be defined outside
void myFunc(int);
void myNamespace::myFunc(int a){
thus structured, the namespace is non-executable and should go into header file

4. Using Namespaces several styles
always use scope resolution operator (explicit statement of scope)
for(int i=0; i < myNamespace::limit; ++i)
myNamespace::myFunc(i);
import a name – specify that you are using a specific name in this file
using myNameSpace::limit;
using myNameSpace::myFunc;
for(int i=0; i < limit; ++i)
myFunc(i);
import all names in a namespace
using namespace myNamespace;
do not do in headers – opens namespace for all source files including this header

5. Scope of Importing
variables can be imported either into global scope or into a block
importing into the global scope – imported variables can be used anywhere
using myNameSpace::limit;
int main(){
for(int i=0; i < limit; ++i)
myFunc(i); }
importing into the scope of a function – imported names can be used inside function only

6. std Namespace has an extensive set of names used in programs. Contains
cout, cin, endl, vector, string, etc.
three styles of using std:
explicit scope resolution of all names
pro: safest
con: program code becomes less terse
import specific names with using
pro: more terse
con: have to maintain name list at beginning of the file
import all names using namespace std;
pro: simplest, tersest
con: unexpected names are imported: sort, find, count are in std; do not use in header files!

7. Namespaces Review
what is the scope of a function? global variable? global constant?
what is name collision? what is a namespace and why is it needed?
how to define a namespace? is namespace executable statement?
how do you define a function declared in a namespace?
the three styles of using namespaces are
explicit namespace resolution
importing specific name
importing all names in a namespace
how do you using each style? what are the advantages/disadvantages of each style?
which style should be used in a header
what happens when using is put inside/outside function definition?