Exercise (FH): Write A Sensor Class: RandomSensor#

New Sensor Class: RandomSensor#

Based on the project you git-cloned in Exercise (FH): Introducing a Sensor Class, extend the sensors library (int src/sensors/) with another sensor, RandomSensor.

Create two new files in that directory,

  • random-sensor.h. That file contains the class definition

  • random-sensor.cpp. That file contains the implementation

The proposed usage of such a sensor is as follows:

double low = 32.4;
double high = 38.7;

RandomSensor sensor{low, high};
double temperature = sensor.get_temperature();

// temperature is a random number between low and high

Here is a sample program that generates random numbers in such a way. It is your responsibility to understand how random numbers are generated, and to write the RandomSensor class accordingly.

c++03-exercise-fh-random-demo.cpp#
#include <random>
#include <iostream>

int main(int argc, char** argv)
{
    if (argc != 3) {
        std::cerr << argv[0] << ": <low> <high>" << std::endl;
        return 1;
    }

    double low = std::stod(argv[1]);
    double high = std::stod(argv[2]);

    std::uniform_real_distribution<double> distribution(low, high);  // <--- HERE
    std::default_random_engine engine{std::random_device{}()};       // <--- HERE

    while (true) {
        double number = distribution(engine);                        // <--- HERE
        std::cout << number << std::endl;
    }

    return 0;
}

Implementation Details#

Like in the program above which uses two variables,

std::uniform_real_distribution<double> distribution(low, high);
std::default_random_engine engine;

… the RandomSensor class will have to have two members,

class RandomSensor
{
    // ...
private:
    std::uniform_real_distribution<double> _distribution;
    std::default_random_engine _engine;
};

The RandomSensor::get_temperature() method uses these members to generate random numbers in the specified range - exactly like the program, but nicely encapsulated inside the method implementation.

The RandomSensor constructor - RandomSensor(double low, double high) - passes its arguments to the constructor of the _distribution member in the initializer list.

See this in analogy to the class point example in A Live-Hacked Tour Around The New C++, where we initialize int members (and not random distributions),

class point
{
public:
    point(int x, int y) : _x{x}, _y{y} {}
    ...
};

New Program: random-temperature.cpp#

In the firstname.lastname directory you created for Exercise (FH): Introducing a Sensor Class, create a new program, random-temperature.cpp that works just like this one, but differs in the following ways:

  • It uses your RandomSensor implementation (and not the W1Sensor)

  • It takes from the commandline the necessary low and high parameters to instantiate the RandomSensor object (instead of the filename parameter that the W1Sensor program uses). The interval parameter is still necessary.

    $ ./random-temperature 10.5 30.1 1
... spits out random numbers in the range [10.5, 30.1] every second ...