Writing a wrapper for OLED SSD1306

Question

I'm struggling to learn Arduino's C++ right now. I'm trying to write a simple wrapper so I can use multiple OLED's on my project. Here is what I've got so far :

class Screen
{
  private:
    Adafruit_SSD1306 display;
    unsigned long startTime = 0;

  public :
    Screen(){
       Adafruit_SSD1306 this->display(128, 64, &Wire, -1);
    }
    void init(){
        //Initialize the screen
        this->display.begin(SSD1306_SWITCHCAPVCC, 0x3C);
        this->display.setTextSize(1);
        this->display.setTextColor(SSD1306_WHITE);
        this->display.clearDisplay();
        this->output(60,30,":)");
        this->display.display();
    }

    void output(int x, int y, String S){
      this->display.setCursor(x, y);
      this->display.print(S);
      Display.display();
    }
};


Screen screen();
void setup(){
  screen.init();
}

void loop(){}

Errors are :

In file included from D:\project\escape\puzzle box\source\puzzle_box_v6\Puzzle_box_v6.ino:12:0:
sketch\Screen.h: In constructor 'Screen::Screen()':
Screen.h:12:25: error: expected unqualified-id before 'this'
        Adafruit_SSD1306 this->display(128, 64, &Wire, -1);
                         ^~~~
sketch\Screen.h: In member function 'void Screen::output(int, int, String)':
Screen.h:27:7: error: 'Display' was not declared in this scope
       Display.display();
       ^~~~~~~
sketch\Screen.h:27:7: note: suggested alternative: 'display'
       Display.display();
       ^~~~~~~
       display
D:\project\escape\puzzle box\source\puzzle_box_v6\Puzzle_box_v6.ino: In function 'void setup()':
Puzzle_box_v6:40:9: error: expected unqualified-id before '.' token
   Screen.init();
         ^
exit status 1
expected unqualified-id before 'this'

I would appreciate any and all advice. Perhaps my entire approach is wrong. If not, specifically could I get an explanation on how to generate an object and assign it to a property of another class.

Lastly, if anyone is still reading...I don't what parameter data type I need to declare to pass in the memory location value for init(). Currently it is "0x36" hardcoded, I want to pass it in via parameter. If anyone could advise on this matter I would appreciate it as well.

Answer 1

I am not sure if I understand your intentions, but I suppose you wanted to initialize the display member when you wrote

Adafruit_SSD1306 this->display(128, 64, &Wire, -1);

in the constructor. The thing is: This line makes no sense.

To initialize the member by calling its constructor you should use the member initialization list. Also init should probably be part of Screens constructor:

Screen() : display(123,64, &Wire, -1) {
    //Initialize the screen
    display.begin(SSD1306_SWITCHCAPVCC, 0x3C);
    display.setTextSize(1);
    display.setTextColor(SSD1306_WHITE);
    display.clearDisplay();
    output(60,30,":)");
    display.display();
}

You don't need to prefix members with this->. Not sure what &Wire is, as its not part of the error message I suppose it is declared in code you did'nt post.

Other errors are 'Display' was not declared in this scope because there is no Display. If you wanted to call the method display of the Adafruit_SSD1306 member you have to pay attention to capitalization: display.display();

Screen screen(); is the so-called most vexing parse. It declares a function. If you want to declare an object of type Screen write this instead:

 Screen screen;          // or ..
 Screen screen{};        // or...
 auto screen = Screen();

The last error is not in the code you posted. It complains about Screen.init() while your have the correct screen.init();. Though, as mentioned above, initialization should probably be part of constructing a Screen and you can remove the method and that call.

Answer 2

This line:

Adafruit_SSD1306 this->display(128, 64, &Wire, -1);

is not valid C++. If you want to initialise the display member in your Screen object, you can do something like:

this->display = Adafruit_SSD1306 (128, 64, &Wire, -1);

Disclaimer: I don't know what parameters the Adafruit_SSD1306 constructor is expecting, so the above might need to be tweaked a little.

Alternatively (and better), you can initialise your display member in Screens constructor's initialisation list, as described in @largest_prime's answer. If you don't want to initialise display with all constants then pass any necessary arguments to Screen's constructor in either case.

Also, you don't need to write this-> all over the place. This is assumed by the compiler.