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C++ Programming Code Examples

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Namespaces in C++ Programming Language

Namespaces in C++ Language
Consider a situation, when we have two persons with the same name, jhon, in the same class. Whenever we need to differentiate them definitely we would have to use some additional information along with their name, like either the area, if they live in different area or their mother's or father's name, etc. Same situation can arise in your C++ applications. For example, you might be writing some code that has a function called xyz() and there is another library available which is also having same function xyz(). Now the compiler has no way of knowing which version of xyz() function you are referring to within your code. A namespace is designed to overcome this difficulty and is used as additional information to differentiate similar functions, classes, variables etc. with the same name available in different libraries. Using namespace, you can define the context in which names are defined. In essence, a namespace defines a scope.
Defining a Namespace
A namespace definition begins with the keyword namespace followed by the namespace name as follows:
namespace namespace_name { // code declarations }
To call the namespace-enabled version of either function or variable, prepend (::) the namespace name as follows:
name::code; // code could be variable or function.
Using Directive
You can also avoid prepending of namespaces with the using namespace directive. This directive tells the compiler that the subsequent code is making use of names in the specified namespace.
Discontiguous Namespaces
A namespace can be defined in several parts and so a namespace is made up of the sum of its separately defined parts. The separate parts of a namespace can be spread over multiple files. So, if one part of the namespace requires a name defined in another file, that name must still be declared. Writing a following namespace definition either defines a new namespace or adds new elements to an existing one:
namespace namespace_name { // code declarations }
Nested Namespaces
Namespaces can be nested where you can define one namespace inside another name space as follows:
namespace namespace_name1 { // code declarations namespace namespace_name2 { // code declarations } }
• Namespace is a feature added in C++ and not present in C. • A namespace is a declarative region that provides a scope to the identifiers (names of the types, function, variables etc) inside it. • Multiple namespace blocks with the same name are allowed. All declarations within those blocks are declared in the named scope. • Namespace declarations appear only at global scope. • Namespace declarations can be nested within another namespace. • Namespace declarations don't have access specifiers. (Public or private) • No need to give semicolon after the closing brace of definition of namespace. • We can split the definition of namespace over several units.
/* namespaces in C++ language */ // A C++ code to demonstrate that we can define // methods outside namespace. #include <iostream> using namespace std; // Creating a namespace namespace ns { void display(); class happy { public: void display(); }; } // Defining methods of namespace void ns::happy::display() { cout << "ns::happy::display()\n"; } void ns::display() { cout << "ns::display()\n"; } // Driver code int main() { ns::happy obj; ns::display(); obj.display(); return 0; }

Internal method to insert into a subtree. x is the item to insert. t is the node that roots the tree. Set the "New Root". Internal method to remove from subtree. x: the item to remove.

This represents the queue dequeue function. Every time another object or customer enters the line to wait, they join the "end of the line" and represent the "enqueue function". Queue