This plugin loader node loads each plugin and inputs the number to each plugin
and fetch's the result from the plugin. We can locate the calculator_loader.cpp file from the chapter_5_codes/pluginlib_calculator/src folder.

Here is the explanation of this code:

#include <boost/shared_ptr.hpp> 
#include <pluginlib/class_loader.h> 
#include <pluginlib_calculator/calculator_base.h> 

These are the necessary header files to load the plugins:

pluginlib::ClassLoader<calculator_base::calc_functions> 
 calc_loader("pluginlib_calculator", 
 "calculator_base::calc_functions");

The pluginlib provides the ClassLoader class, which is inside class_loader.h, to load classes in runtime. We need to provide a name for the loader and the calculator base class as arguments:

   boost::shared_ptr<calculator_base::calc_functions> add = 
 calc_loader.createInstance("pluginlib_calculator/Add");

This will create an instance of the Add class using the ClassLoader object:

    add->get_numbers(10.0,10.0); 
    double result = add->operation(); 

These lines give an input and perform the operations in the plugin instance.