Exercise (FH): Introducing a Sensor Class¶

The project is built just the same as we used to build our previous toy projects - its just that the project structure is a bit more involved. Each directory that participates in the build contains a CMakeLists.txt file,

FH-ECE20
├── bin
│   └── CMakeLists.txt
├── CMakeLists.txt
├── googletest
│   ├── CMakeLists.txt
│   └── googletest
│       ├── CMakeLists.txt
├── src
│   ├── CMakeLists.txt
│   ├── c++-school
│   │   └── CMakeLists.txt
│   └── sensors
│       └── CMakeLists.txt
└── tests
    └── CMakeLists.txt

Dependencies/Usage Relationships ¶

Executables: ADD_EXECUTABLE()
Libraries: ADD_LIBRARY()
Dependency relationship: TARGET_LINK_LIBRARIES()

digraph foo {
"onewire-temperature" -> "sensors";
"run-tests" -> "sensors";
}

Onewire Sensor Usage: Example/Unit-Test ¶

From w1-sensor-suite.cpp:

#include <w1-sensor.h>

...

std::string filename = "/sys/bus/w1/devices/28-02131d959eaa/temperature"; // for example
W1Sensor sensor{filename};                     // instantiate W1Sensor
double temperature = sensor.get_temperature(); // ask it to read temperature

Requirement ¶

Step 1: Preparation ¶

Clone the Github project (see instructions on main page (scroll to bottom))
Create a new subdirectory firstname.lastname (e.g. joerg.faschingbauer) of the toplevel project directory
Modify the toplevel CMakeLists.txt to descend into that new subdirectory (you’ll find out how that is done by looking at the CMakeLists.txt file)
In your subdirectory …
- create a file onewire-temperature-<firstname>-<lastname>.cpp, which is a copy of bin/onewire-temperature.c
- Add a CMakeLists.txt file that builds that into an executable onewire-temperature-<firstname>-<lastname>

Step 2: Modify `onewire-temperature-<firstname>-<lastname>.cpp` To Use `class W1Sensor`¶

Rip everything out that implements the reading of the sensor file
Use class W1Sensor instead:
- Look into w1-sensor-suite.cpp
- See how W1Sensor is instantiated
- See how W1Sensor is used to read the temperature
- Do the same in your program: use W1Sensor to implement what you just ripped out
- As you go, modify the program’s output to show real floatingpoint degrees in Celsius (and not integer millidegrees). You simply say,
```
#include <iostream>
...
std::cout << temperature << std::endl;
```

Note

W1Sensor is defined in src/sensors/. Look into that directory’s CMakeLists.txt file: it builds a (static) library sensors.

Your program uses W1Sensor, so you will have to link your program against the sensors library, by using CMake’s target_link_libraries() function. See tests/CMakeLists.txt for an example.

Step 3: Answer A Question ¶

Has the program become more readable?

Navigation

Exercise (FH): Introducing a Sensor Class¶

Github Project ¶

Structure ¶

CMake Build ¶