Namespaces

Recall that in object-oriented programming, we can group variables and functions into a class. A more general container is a namespace. We can group code into a namespace to prevent confusion. The most common namespace we will use in the following materials is std, the C++ standard library. This library contains numerous methods and variables, including but not limited to: cout, vector, queue, and many more.

Here are some examples of name spaces:

// The Cube.h file
#pragma once

namespace einLib {
	class Cube {
		public:
			double getVolume();
			double getSurfaceArea();

		private:
			double length_;
	}
}

// The Cube.cpp file
#include "Cube.h"

namespace einLib {
	double Cube::getVolume() {
		return length_ * length_ * length_;
	}
	double Cube::getSurfaceArea() {
		return 6 * length_ * length_;
	}
}

The namespace keyword tells C++, "Everything inside the curly braces following einLib belongs to the namespace einLib. Now, the class Cube is no longer class simply called Cube. We've now added more specificity: einLib::Cube.

We can now use the code above to write a program:

#include "Cube.h"
#include <iostream>

int main() {
	einLib::Cube c;
	std::cout << "Volume: " << c.getVolume() << std::endl;
	return
}

Takeaway: The whole idea behind namespacing is to define scope. It helps avoid collisions between entities of the same name. C++ has so many short identifiers that we need a way to differentiate between all of them. Namespaces are the means of ensuring that differentiation. We can directly write namespaces inside our source code:

include <iostream>

namespace foo {
	double e = 1.718;
}

int main() {
	double e = 2.0;
	double a = foo:e + 3.0; // evaluates to 4.718
	double b = e + 3.0; // evaluates to 5.0
}