Question

I have an assignment to learn how to use boost::variant. I’m trying to create a function that asks the user for a shape type to create. Then create the requested shape and assign it to the variant and return it. I’m using a switch to accomplish this, but I’m getting a runtime error with the default statement.

I also get a warning from the compiler: “warning C4715: ‘ShapeVariant’ : not all control paths return a value”

How do I just print a string if the user enters an invalid selection?

Thanks!

#include "boost/variant.hpp"

typedef boost::variant<Point,Line,Circle> ShapeType;

ShapeType ShapeVariant()
{
    cout << "Please select a Shape Type\n1: Point\n2: Line\n3: Circle\n\nSelection: ";

    int choice;

    cin >> choice;

    switch(choice)
    {
    case 1: return Point(); break;
    case 2: return Line(); break;
    case 3: return Circle(); break;
    default: cout << "Invalid selection." << endl; break;
    }   
}

Answer 1

Instead of printing a string from the function, you could instead throw an exception that the caller catches and prints the reason why the exception was thrown.

switch(choice)
{
  case 1: return Point(); break;
  case 2: return Line(); break;
  case 3: return Circle(); break;
  default: throw std::runtime_error( "Invalid selection." );
} 

In the caller:

try {
  auto result = ShapeVariant();
} catch( std::exception const& e ) {
  std::cout << e.what() << std::endl;
}