Namespaces

Chapter 7

What does this statement, using namespace std; do and what similar statements can we use? Find out here!

Problems with conflicting global identifiers (constants, functions, enum types, etc.):

Global identifiers in a header file used in a program become global in the program
- A syntax error occurs if an identifier has the same name as a global identifier in the header file
The same problem can occur with third-party libraries
- Common solution: third-party vendors begin their global identifiers with _ (underscore)
  Do not begin identifiers in your program with _

Namespaces attempt to solve these problems.

A namespace includes members, which have a scope that is local to the namespace.

Syntax to create a namespace:

cpp

namespace NamespaceName // NamespaceName can be any identifier you want
{
    // Put here: variable declarations, named constants, functions, 
    // or another namespace

    const int MAX_SIZE = 100; // Example Constant
    
    int calculateSize();    // Example function prototype; definitions go
                            // below the namespace (and below main)
} // <-- No semicolon here

int NamespaceName::calculateSize()  // Example function definition
{
    // ...
}

A namespace member can be accessed outside the namespace:
cpp
```
NamespaceName::identifier;
```
1
Or the identifier can be used without specifying the namespace if you use:
cpp
```
using namespace NamespaceName;
```
1
Or for just the specific identifier.
cpp
```
using NamespaceName::MAX_SIZE;
```
1
After the using statement, it is NOT necessary to put the NamespaceName:: before the namespace member.
Unless a namespace member and a global identifier or a block identifier have the same name.
Example for defining a function with a prototype in a namespace (below main).
(See the example of calculateSize() above).

Namespaces ​

Namespaces