1

I'm having troubles understanding the inner workings of classes and such.

I have a class called Attributes that contains parameters. In my .ino, I can simply instantiate an object with Attributes greenBark(1, 2); and everything is hunkey dorey.

Problem: Now I need to create a Attributes object in my other class, called Tree. I figured out if my constructor doesn't have parameters, I can create an object within another class just fine. However, my attributes class constructor has parameters. When I try to create an parameterized object within another class, the compiler tosses an error. How can I create an attributes object within my tree class? I'm sorry if I got some of these terms mixed up, I'm trying to keep up!

Here are my current files (made for this example:)

The .ino file

#include "attributes.h"
#include "tree.h"

Attributes greenBark(1, 2);

void setup()
{
  Serial.begin(9600);
}

void loop()

{
  greenBark.printAttributes();
}

attributes.cpp

#include "attributes.h"

Attributes::Attributes(int size, int texture)

{
  _size = size;
  _texture = texture;  
}

void Attributes::printAttributes()
{
  Serial.print("GreenBark Attributes: ");
  Serial.print("Size = ");
  Serial.print(_size);
  Serial.print(" Texure = ");
  Serial.print(_texture);
  Serial.println();
}

attributes.h

#pragma once
#include <Arduino.h>

class Attributes
{
  public:
    Attributes(int size, int texture); // constructor    
    void printAttributes(); // method

  private:
    int _size = 0;
    int _texture = 0;
};

tree.cpp

#include "attributes.h"
#include "tree.h"

Tree::Tree()
{

}

tree.h

#pragma once
#include <Arduino.h>
#include "attributes.h"

class Tree
{
  public:
    
    Tree(); // constructor
    
    void makeTree(); // method

    // I want to create an attributes class object in my current class, so naturally I'd try to
    // create the object just like I did in my .ino sketch, but the below line doesn't work.
    
    //Attributes redBark(1, 2);

  private:  
};

The error provided is this:

In file included from C:\Users\ajrob\Dropbox\Projects\Electronics\Arduino Sketchbook\ParameterizedConstructor\ParameterizedConstructor.ino:2:0:
C:\Users\ajrob\Dropbox\Projects\Electronics\Arduino Sketchbook\ParameterizedConstructor\tree.h:16:24: error: expected identifier before numeric constant
     Attributes redBark(1, 2);
                        ^
C:\Users\ajrob\Dropbox\Projects\Electronics\Arduino Sketchbook\ParameterizedConstructor\tree.h:16:24: error: expected ',' or '...' before numeric constant
In file included from C:\Users\ajrob\Dropbox\Projects\Electronics\Arduino Sketchbook\ParameterizedConstructor\tree.cpp:2:0:
C:\Users\ajrob\Dropbox\Projects\Electronics\Arduino Sketchbook\ParameterizedConstructor\tree.h:16:24: error: expected identifier before numeric constant
     Attributes redBark(1, 2);
                        ^
C:\Users\ajrob\Dropbox\Projects\Electronics\Arduino Sketchbook\ParameterizedConstructor\tree.h:16:24: error: expected ',' or '...' before numeric constant

exit status 1

Compilation error: expected identifier before numeric constant
5
  • en.cppreference.com/w/cpp/language/constructor
    – Juraj
    Feb 24, 2023 at 18:56
  • @Juraj I read that page over a few times understanding what I could and I'm not seeing how it helps my situation Feb 24, 2023 at 19:15
  • 1
    I don't understand much of it either, so I tried Attributes redBark {1, 2}; and it did not throw an error ... I have no idea if it does what you are expecting ... Attributes redBark {1}; and Attributes redBark {1, 2, 3}; both throw an error, so it might be what you want
    – jsotola
    Feb 24, 2023 at 20:04
  • 1
    @AJ_Smoothie your post is not Arduino specific, and really is a general programming question ... it belongs at stackoverflow.com/questions
    – jsotola
    Feb 24, 2023 at 20:19
  • @jsotola I tried the braces in my actual code (the parameters are input pins and default pin states) and it worked out just great. Thank you Feb 27, 2023 at 15:39

1 Answer 1

0

I see two options here:

You might follow jsotola's comment and initialize redBark with braces:

Attributes redBark{1, 2};

For some reason, the syntax with parentheses is not allowed when initializing an object in a class declaration, but the syntax with braces is OK.

The other option is to initialize redBark in the Tree's constructor (and not in the class declaration) using an initializer list:

// In the class declaration:
Attributes redBark;

// The constructor:
Tree::Tree() : redBark(1, 2) {}
1
  • Using the curly braces worked out just fine! Thank you! Feb 27, 2023 at 15:36

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