Passing optional parameter by reference in c++

Question

I\'m having a problem with optional function parameter in C++

What I\'m trying to do is to write function with optional parameter which is passed by reference, so th

Answer 1

Another way to do this is to use pointers instead of references. This provides the semantics that you want without overloading. (Personally, I'd probably go with overloading.)

void foo(double* bar, double* foobar = 0)
{
   if (bar) *bar = 100;
   if (foobar) *foobar = 150;
}

   // ...

   foo(&mBar, &mFoobar);

   // ...

   foo(&mBar);

   // ...

Answer 2

This is how I solved this question:

My original function didn't have a returned error string: bool MyClass::validateXML(const QString& fileName, const QUri& schemaUri);

I wanted to add the results of the validation in an error string so I implemented: bool MyClass::validateXML(const QString& fileName, const QUri& schemaUri, QString& errorString = *(std::make_unique().get()));

This way, you can reference the errorString in validateXML without checking if it's valid, and no memory leaks.

Answer 3

Why can't you use function overloading? Surely it's the easiest solution to your problem?

void foo(double &bar, double &foobar) 
{ 
   bar = 100; 
   foobar = 150; 
}

void foo(double &bar) 
{ 
   double foobar = 0.0;
   foo(bar, foobar);
}

Answer 4

Speaking in terms of Object Oriented paradigm: If given class has and "Default", this Default must declared accordingly, and then may be used as an "Default Parameter" Ex:

class Pagination {
private:
    int currentPage;
public:

    //...
    Pagination() {
        currentPage = 1;
        //...
    }

    // your Default Pagination (Must be initialized before thread concurrency)
    static Pagination& Default() {
        static Pagination p; 
        return p;
    }
};

On your Method ...

     //...
     std::vector<User>
     findByFilter(User& audit, Pagination& p = Pagination::Default() ) {
     // ...

Edited: This solution is quite suitable since in this case it is an "global default" Pagination and a single "reference" value. You will also have the power to change default values such as navigation/display preferences and etc.

Edit2: spelling and fixing...