Avoid multiple instances when declaring variables in classes

Using Arduino Programming Questions
1

In my project I've got multiple classes that need time and a LCD display

  1. the class "Screen" which displays the time and date.
  2. the class "Menu" which allows you to change the time and date.

When declaring the variables I ran into an error (multiple instances).

So now i've got this

in Menu.cpp

...
#include <DS3232RTC.h>
DS3232RTC ScreenRTC;
#include <LiquidCrystal_I2C.h>
LiquidCrystal_I2C Screenlcd(0x27, 16, 2);
...
Screen::Screen() {
  Screenlcd.init();
  setSyncProvider(ScreenRTC.get);
}

And in Screen.cpp:

...
#include <DS3232RTC.h>
DS3232RTC MenuRTC;
#include <LiquidCrystal_I2C.h>
LiquidCrystal_I2C Menulcd(0x27, 16, 2);
...
Menu::Menu() {
    Menulcd.init();
    setSyncProvider(MenuRTC.get);
}

Is this the correct way or is there a way to create a single instance which can be used by both of them?

2

Please show the complete code (all files). Please post the full error message; please use code tags for those as well.

It does not make sense to have the same LCD in both files.

3

Let me rephrase the question before it looks like an XY problem...

Theres only one lcd screen and one RTC module which I want to use in both classes.
So the code I provided is only about declaring the LCD and RTC module in two classes.

The code I have now doesn't throw any errors but that doesn't mean it the right way.

4

Hello

Here is an example how you can do that, sorry it's in French but search "lcd" I think you will easily understand. Basically, the lcd is created in the main sketch and initialized normally in setup(), then a reference to this lcd is given to the Moteur class by using

// link LCD to the Moteur class
Moteur::lcd( lcd );
5

Your incomplete post does not provide sufficient insight into the full structure of your code. So, it's impossible to give definitive advise. But, a couple ideas might be ...

  1. Put the RTC in it's own class that has a public function to provide the time ... ie getTime()

  2. Make the RTC global in your main code and pass it to the classes as a refence.

6

Declare the lcd and rtc as static and make sure that they are public so they can be accessed from outside the class.
https://en.cppreference.com/w/cpp/language/static

7

Thanks that was exactly what I was looking for!

8 
DS3232RTC ScreenRTC;
LiquidCrystal_I2C Screenlcd(0x27, 16, 2);

shouldn't both of these lines be in your main .ino/cpp file and presumably there is a (loop).h file containing

extern DS3232RTC         ScreenRTC;
extern LiquidCrystal_I2C Screenlcd;

included in other files as required

9

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