Compile Error Depends on Constructor Used

Using Arduino Programming Questions
#1

Hi All.

After many years a C programmer, I’m finally tackling the intricacies of C++ classes and constructors. This code illustrates the problem I hit:

class myClass {
  private:
    uint16_t y;

  public:
    void printValues();    
    myClass();
    myClass(uint16_t);   
};

myClass::myClass() : y(2) {}
myClass::myClass(uint16_t y) : y(y) {}

void myClass::printValues() {
  Serial.print("y = ");Serial.println(y);
}

myClass classInstance1();
myClass classInstance2(44);

void setup() {
  Serial.begin(115200);
  delay(1000);
  classInstance1.printValues();
}

void loop() {}

The compile-time error message is:

Arduino: 1.8.2 (Windows 10), TD: 1.36, Board: "Arduino/Genuino Uno"

C:\Users\tr001221\Documents\Portable Arduino 1.8.2\arduino-1.8.2\portable\sketchbook\yyy\yyy.ino: In function 'void setup()':

yyy:24: error: request for member 'printValues' in 'classInstance1', which is of non-class type 'myClass()'

   classInstance1.printValues();

                  ^

exit status 1
request for member 'printValues' in 'classInstance1', which is of non-class type 'myClass()'

This report would have more information with
"Show verbose output during compilation"
option enabled in File -> Preferences.

However, if instead I try to call the ‘printValues()’ method on the other class instance:

class myClass {
  private:
    uint16_t y;

  public:
    void printValues();    
    myClass();
    myClass(uint16_t);   
};

myClass::myClass() : y(2) {}
myClass::myClass(uint16_t y) : y(y) {}

void myClass::printValues() {
  Serial.print("y = ");Serial.println(y);
}

myClass classInstance1();
myClass classInstance2(44);

void setup() {
  Serial.begin(115200);
  delay(1000);
  classInstance2.printValues();
}

void loop() {}

It compiles without error.

Would appreciate help with this from an experienced C++ coder.

Thanks.

#2

UPDATE:
Looks like my first instantiation was incorrect. Compiles fine if I do it this way:

myClass classInstance1;

Instead of:

myClass classInstance1();

Will have to wait until later to test it on hardware.

#3

Not sure how you expect anyone to help, when you clearly have NOT posted the part of the code containing the problem...

Regards,
Ray L.

#4

Actually, I did in the very first post:

  • The first </> block in that post contains the code that produces the compile error.

  • The second </> block in that post contains the actual compiler error message(s).

  • The third </> block in that post contains the code that compiles without an error.

In Reply #1 I posted the correction (for the first </> in my original post) that fixed the compile error.

What’s missing?

#5

Additional info. The first </> block in my original post produce the same error for both Uno and Teensy3.2 board selections.

Arduino IDE 1.8.2
Teensyduino 1.36

Anything else required?

#6 
myClass::myClass() : y(2) {}
myClass::myClass(uint16_t y) : y(y) {}

Note: The ": initializers" syntax is required if the target variable is 'const' but for regular variables I find it easier to read and understand a traditional assignment:

myClass::myClass() {y=2;}
myClass::myClass(uint16_t _y) {y=_y;}
#7

Understood.

Turns out either constructor method causes a compile error if I don’t get the syntax right.

In order instantiate a variable using the “no parameter” constructor, it looks like the syntax needs to be:

myClass classInstance1;

It won’t compile if I try this:

myClass classInstance1();

I guess this makes sense, I just thought there might be some symmetry with the versions of the constructor that do take parameter(s). Meaning, if this is OK:

myClass classInstance2(44);

…why is this not OK:

myClass classInstance1();
#8

It's not OK for creating an instance because it looks just like a function prototype for a function that takes no arguments and returns an instance of myClass. Similarly, if the parens contain a declaration then it IS a function prototype:

myClass identifier(int x);
#9

Makes sense. Thanks.

#10