Passing objects to cpp classes

Projects Programming
1

Hi there,

I guess I have a quite simple question for you guys but it drives me nuts. Here is what i want to do or at least it looks like the same in my code.

myclassA.h

#ifndef MYCLASSA
#define MYCLASSA

#include "Arduino.h"

class myclassA
{
  public:
    myclassA();
    void DoSomething(void);
};
#endif

myclassB.h

#ifndef MYCLASSB
#define MYCLASSB

#include "Arduino.h"
#include "myclassA.h"

class myclassB
{
  public:
    myclassB();
    void DoSomething(myclassA& classA);
};
#endif

main code

#include "myclassA.h"
#include "myclassB.h"

myclassA p_classA();
myclassB p_classB();

void setup()
{}

void loop()
{
   p_classB.DoSomething(p_classA);
}

This is just an abstract example of what Iam trying to do, but in my code I get the following error as soon as myclassB::DoSomething(..) has the argument as described above.

no matching function for call to 'myclassB::DoSomething(myclassA (&)())'

What the hell I am doing wrong?

What is the compiler trying to tell me with the "(&)()" in the error message?

2

The line

void DoSomething(myclassA& classA);

is a method declaration only. Where your definition of it??

3

I only posted an "abstract" of my code. There are also cpp files with the corresponding implementation of the function.
Does this answer the question?

4

This code compiles fine for me:

class myclassA
{
  public:
    myclassA() {};
    void DoSomething(void);
};
class myclassB
{
  public:
    myclassB() {};
    void DoSomething(myclassA& classA) {};
};

myclassA p_classA;
myclassB p_classB;

void setup()
{}

void loop()
{
   p_classB.DoSomething(p_classA);
}

I added implementations to the constructors and methods and removed empty braces after object instantes.

I use Arduino v1.8.19

5

I think this is the problem (you declare a function that takes no arguments and returns an object of type myclassA).

6

This is a common mistake:

If the constructor takes no arguments you CAN'T use the empty parentheses: (). If there is a type declaration in the parens the compiler knows you are declaring a function with an argument. If there is a value in the parens the compiler knows you are calling a function. When there is nothing in the parens the compiler can't tell for sure so it defaults to declaring a function, but you want to call the constructor, not declare it. You have to leave the parens out.

7

Oh wow. That was the problem. Thank you so much.

But just to understand this. I am telling the compiler that I want to create an object of the type myClassA, so he should know that I declared a constructor for it, shouldn't he?

8

Thanks so much. That was the problem!

9

Yes it does, but what if you wanted to declare a function that returns an object of type myclassA?

Perhaps you can mark the most helpful post as the solution then? This prevents helpers spending time on a solved issue and it will lead people with the same question to the correct answer directly.

10

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