C++ Implementation File (.cpp)

An implementation file (.cpp) contains the code to implement the class (or other C++ code).

cpp-class/Cube.cpp

#include "Cube.h"            // << Header file

double Cube::getVolume(){                // << Define method
	return length_ * length_ * length_;
}

double Cube::getSurfaceArea(){           // << Define method
	return 6 * length_ * length_;
}

void Cube::setLength(double length){      // << Define method
	length_ = length;
}

The #include "Cube.h" adds the library where the Cube class, with its methods and variables (or members).

You might have spotted the :: syntax; in short, this means that the getVolume() function belongs to the Cube class.

Let's make a program with our class!

cpp-class/main.cpp

#include "Cube.h"            // << Header file

int main(){                  // Staring point of all C++ programs
	Cube c;

	c.setLength(3.48);
	double volume = c.getVolume();
	std::cout << "Volume: " << volume << std::endl;

	return 0;
}

The output of this program is:

user@host:~$ cd cpp-class

user@host:~/cpp-class$ make
clang++ -std=c++ly -stdlib=libc++ -O0 -pedantic -Wall -Werror -Wfatal-errors -Wextra -Who-unused-parameter -Who-unused-variable -MMD -MP -g -c main.cpp -o .objs/main.o
clang++ .objs/main.o .objs/Cube.o -std=c++ly -stdlib=lib++ -o main

user@host:~/cpp-class$ ./main
Volume: 42.1442

user@host:~/cpp-class$

Success!!