Calling a Function with integer [[mayb_unused]] macro and default argument boolean type parameter

Question

I am writing a Function with 2 Parameters, 1st is integer type marked [[maybe_unused]] and 2nd is Boolean Type with Default Argument false.

int preOrderTraversial([[maybe_unused]] int searchData, bool forDisplay = false)

This is the function declaration. The function is used for pre-order Traversal in Binary Search Tree. I want to use the same function for Displaying the Tree and Traversing it for searching a Node with specific Data. But only for 1 of both problems at once. Not for searching AND displaying you see.

So, obviously, it works fine for the searching part but when I call the function for Displaying the function call looks like this:

preOrderTraversal(true)

or

bool forDisplay = true;
preOrderTraversal(forDisplay);

Now the Compiler (even with the parameter DECLARED as a BOOL) still considers this bool parameter as an int and uses it for searchData (integer) parameter of the function and not for the forDisplay (bool) parameter.

Is there a way to force or tell compiler which of both parameters I am trying to work with?

Answer 1

[[maybe_unused]] means that the function body may not use it, but the signature of the function always have it. Actually event the default value for the boolean does not modify the signature of your function; Thus your function always take 2 arguments, the first being a integer, and the second being a boolean (that may be set to the default if you didn't put it). You end up with calling:

bool forDisplay = true;
preOrderTraversal(/* integer searchData; bool geting casted to int */ forDisplay,
                  false /* the forDisplay (2nd param) default value*/);

which does not meet your expectations.

[EDIT] how to overcome? There is not builtin way to use named parameters in C++ but you may workaround using a helper class:

struct PreOrderTraversal {
  bool _forDisplay = false;
  int _searchData = 0; /* FIXME What is the default here? */
  auto& forDisplay() { _forDisplay = true; return *this; }
  auto& searchData(int x) { _searchData = x; return *this; }

  void run() { if (_forDisplay) ;//do the right things
               else ;// use data

  }
};

then you can use it with:

PreOrderTraversal().forDisplay().run();
PreOrderTraversal().searchData(123).run();

This kinda mimics that named parameter feature.