How to Extend existing enums

Picked up this very interesting example on extending enum's. The program is self explanatory and is as follows:

//Program tested on Microsoft Visual Studio 2008 - Zahid Ghadialy
#include<iostream>

using namespace std;

int main()
{
  enum Enum1
  {
    value1,
    value2,
    value3,
    final_value = value3
  };

  //Print out the enum values
  cout<<"Enum1 values : ";
  for(int i = 0; i <= final_value; i++)
    cout<<Enum1(i)<<" ";
  cout<<endl;

  enum extendedEnum1
  {
    value4 = final_value + 1,
    value5,
    value6,
    new_final_value = value6
  };

  //Print out the enum values
  cout<<"extendedEnum1 values : ";
  for(int i = 0; i <= new_final_value; i++)
    cout<<extendedEnum1(i)<<" ";
  cout<<endl;

  return 0;
}

The output is as follows:

Via: Learning C++: Extending enums

Extending enums

There might come a scenario where you want to include an enum into a another one where the first one is a subset.

#include
struct enum_a {
     enum constant {
         a, b, c, d,
         end_of_enum_a = d
     };
};
struct enum_b : public enum_a {
     enum constant {
         e = end_of_enum_a + 1,
         f, g, h
     };
};
int main() {
     std::printf("enum_a: a(%d), b(%d), c(%d), d(%d)\n",
         enum_b::a, enum_b::b, enum_b::c, enum_b::d);
     std::printf("enum_b: e(%d), f(%d), g(%d), h(%d)\n",
         enum_b::e, enum_b::f, enum_b::g, enum_b::h);
     return 0;
}

Inheritance to the rescue. :-)

Simple example of BitSets in C++

From "The C++ Standard Library" By Nicolai M Josuttis: A bitset is a bitfield with an arbitrary but fixed number of bits. You can consider it a container for bits or Boolean values. Note that the C++ standard library also provides a special container with a variable size for Boolean values: vector.

Lets write a simple program using rainbow colours.

//Program tested on Microsoft Visual Studio 2008 - Zahid Ghadialy
//Simple example of BitSets
#include<iostream>
#include<bitset>

using namespace std;

int main()
{
  enum Colour {red, orange, yellow, green, blue, indigo, violet, numOfColours};

  bitset<numOfColours> usedColours;

  usedColours.set(red);
  usedColours.set(blue);

  //Lets see the output
  cout << "bitfield of used colours: " << usedColours << endl;
  cout << "number of used colors: " << usedColours.count() << endl;
  cout << "bitfield of unused colors: " << ~usedColours << endl;

  //If any colour is used
  if (usedColours.any())
  {
    // loop over all colors
    for (int c = 0; c < numOfColours; ++c)
      if (usedColours[(Colour)c])
        cout << Colour(c)<< " used "<<endl; //No way to print enum names directly
  }

  return 0;
}

The output is as follows:


Reference: