still struggling with c++ syntax :)

[Gripporillat]

Hi everybody!

I'm trying to create a no-arguments-provided-version of a class constructor, this is my code:

//empty Constructor
SkyFlash::SkyFlash(): poti(SkyPoti()), bounce(0, 0) {
}

//Constructor
SkyFlash::SkyFlash(SkyPoti& Poti, int pin) : poti(Poti), bounce(pin, 10) {
	pinMode(pin, INPUT_PULLUP);
	
}

and this is the error message:

Arduino: 1.8.8 (Windows 10), TD: 1.45, Board: "Teensy 3.5, MIDI, 120 MHz, Faster, US English"

...\libraries\SkyController\SkyFlash.cpp: In constructor 'SkyFlash::SkyFlash()':

...\libraries\SkyController\SkyFlash.cpp:7:51: error: invalid initialization of non-const reference of type 'SkyPoti&' from an rvalue of type 'SkyPoti'

SkyFlash::SkyFlash(): poti(SkyPoti()), bounce(0, 0) {

^

Your help will be highly appreciated!
Robert

P.S.: You can find the whole project in the .zip file

 

[defragster]

Can you post a simple example to cut/paste into the IDE without needing zip download/extract …

Does this cover the intent? correct-way-of-initializing-a-struct-in-a-class-constructor

 

[Gripporillat]

Can you post a simple example to cut/paste into the IDE without needing zip download/extract …

Ok. This compiles:

class testclass1 {
  public:
    testclass1 ();
  private:
};

testclass1::testclass1 () {
}


class testclass2 {
  public: 
    testclass2(testclass1& test);
    
  private:
    testclass1& _test;
};

testclass2::testclass2(testclass1& test): _test(test) {
  
}


void setup() {
  // put your setup code here, to run once:

}

void loop() {
  // put your main code here, to run repeatedly:

}

while this unfortunately doesn't compile:

class testclass1 {
  public:
    testclass1 ();
  private:
};

testclass1::testclass1 () {
}


class testclass2 {
  public: 
    testclass2();
    testclass2(testclass1& test);
    
  private:
    testclass1& _test;
};

testclass2::testclass2() {
  
}

testclass2::testclass2(testclass1& test): _test(test) {
  
}


void setup() {
  // put your setup code here, to run once:

}

void loop() {
  // put your main code here, to run repeatedly:

}

I have to somehow initialize _test without giving the constructor an argument. I tried:

class testclass1 {
  public:
    testclass1 ();
  private:
};

testclass1::testclass1 () {
}


class testclass2 {
  public: 
    testclass2();
    testclass2(testclass1& test);
    
  private:
    testclass1& _test;
};

testclass2::testclass2() : _test(testclass1()) {
  
}

testclass2::testclass2(testclass1& test): _test(test) {
  
}


void setup() {
  // put your setup code here, to run once:

}

void loop() {
  // put your main code here, to run repeatedly:

}

But that doesn't work either.

 

[defragster]

Was the link ... added after initial posting … on point? The second example seemed relevant.

IIRC - in this environment it was found that doing things [calling code outside your code?] in the constructor is problematic and IIRC was best done in a .begin() in setup() after the machine was ready to run.

 

[Gripporillat]

To be honest, I don't fully understand the content of your link and I don't exactly get how it relates to my problem.

First I had the equivalent to this code:

class testclass1 {
  public:
    testclass1 ();
  private:
};

testclass1::testclass1 () {
}


class testclass2 {
  public: 
    testclass2(testclass1& test);
    
  private:
    testclass1& _test;
};

testclass2::testclass2(testclass1& test): _test(test) {
  
}


void setup() {
  // put your setup code here, to run once:

}

void loop() {
  // put your main code here, to run repeatedly:

}

and it nicely worked. But now I need a default constructor. It doesn't need to create a working object, I just need it as a dummy to initialize an array of objects. But I don't know how to write this default constructor without changing the rest of the code.

 

[PaulStoffregen]

Maybe like this? (does compile)

class testclass1 {
  public:
    testclass1 ();
  private:
};

testclass1::testclass1 () {
}


testclass1 default_instance_of_testclass1;


class testclass2 {
  public: 
    testclass2();
    testclass2(testclass1& test);
    
  private:
    testclass1& _test;
};

testclass2::testclass2() : _test(default_instance_of_testclass1) {
  
}

testclass2::testclass2(testclass1& test): _test(test) {
  
}


void setup() {
  // put your setup code here, to run once:

}

void loop() {
  // put your main code here, to run repeatedly:

}

 

[Gripporillat]

Maybe like this? (does compile)

Simple but effective. Thank you! Again.

 

[gfvalvo]

The whole mess can be avoided by not trying to have a member variable that's a reference to a 'testclass1' object. Use a pointer instead. Then you can have a separate member function to set the pointer as desired - regardless of which construct was used to originally create the object:

class testclass1 {
  public:
    testclass1 ();
  private:
};

testclass1::testclass1 () {
}

class testclass2 {
  public:
    testclass2();
    testclass2(testclass1& test);
    void setPointer(testclass1& test);

  private:
    testclass1 *_test = nullptr;
};

testclass2::testclass2() {
}

testclass2::testclass2(testclass1 &test): _test(&test) {
}

void testclass2::setPointer(testclass1 &test) {
  _test = &test;
}

void setup() {
}

void loop() {
}

BTW, next time you post example code, PLEASE try to use identifiers that don't all look so similar: testclass1, testclass2, test, _test, etc. Use a little imagination!