Clockbusters

Bin eben durch Zufall auf dieses nette, kleine Spiel gestolpert: Es geht darum, 50 Filme anhand von jeweils drei Bildern zu erkennen. Man hat für jeden Film 60 Sekunden Zeit. Also Filmfans, versucht euch mal.

Hier geht’s zum Clockbuster-Spiel

clockbuster

Als Hilfe empfiehlt sich natürlich imdb.com, da die Filmtitel auf englisch eingegeben werden müssen.

clockbusters

C++ and virtual methods (for C# or Java programmers)

Last friday I stumbled over a seroius shortcomming of C++ (compared to C# or Java) I’d like to share here with you. It’s about virtual methods called from a class constructor.

The C# Example

Let me start with an example. Here’s some C# code that simply calls a virtual method (named test()) from the class’ constructor:

class TestBaseClass {
  public TestBaseClass() {
    Console.Write("From base class: ");
    test();
  }

  protected virtual void test() {
    Console.WriteLine("in base class");
  }
}

Creating an instance of this class results in nothing special:

From base class: in base class

Now lets create a sub class of TestBaseClass and override the virtual method:

class TestSubClass : TestBaseClass {
  public TestSubClass() {
    Console.Write("From sub class: ");
    test();
  }

  protected override void test() {
    Console.WriteLine("in sub class");
  }
}

Now, creating an instance of TestSubClass will print this:

From base class: in sub class
From sub class: in sub class

This means that the sub class’ implementation of test() was executed (and not TestBaseClass‘ implementation) – just as expected.

Note: In Java all methods are automatically virtual. In contrast to C# or C++ you can’t create “non-virtual” methods in Java.

The C++ Problem

And exactly here is the problem in C++. Let’s create a C++ version of the two classes above (compiled with Visual C++).

Header file (TestClass.h):

#pragma once

class TestBaseClass {
public:
  TestBaseClass();

protected:
  virtual void test();
};


class TestSubClass : public TestBaseClass {
public:
  TestSubClass();

protected:
  virtual void test();
};

Source file (TestClass.cpp):

#include "TestClass.h"
#include <stdio.h>

TestBaseClass::TestBaseClass() {
  printf("From base class: ");
  test();
}

void TestBaseClass::test() {
  printf("in base class\n");
}


TestSubClass::TestSubClass() : TestBaseClass() {
  printf("From sub class: ");
  test();
}

void TestSubClass::test() {
  printf("in sub class\n");
}

Now, creating an instance of TestSubClass results in the following output:

From base class: in base class
From sub class: in sub class

Note how the base class’ implementation of test() is used in the base class constructor while the sub class’ implementation of test() is used in the sub class constructor.

The problem here (in constrast to C# or Java) is that the sub class constructor hasn’t been executed yet and therefore the “redirection” from TestBaseClass::test() to TestSubClass::test() hasn’t been established yet.

Rule: There is no way to call a sub class’ implementation of a virtual function in the base class constructor!

The problem becomes even more severe with pure virtual (which is abstract in C# and Java) methods. These methods don’t even have an implementation in the base class and therefore can’t be executed at all.

For your interest: A C++/CLI class will behave like a C# class (and not like a C++ class).

Example Visual Studio Solution

I’ve created a solution (for Visual Studio 2010) containing the source code above. In addition to a C# and a C++ project, I’ve also added a C++/CLI project. You can download it here:

VirtualMethodTest.zip

How to add a radio station to iTunes

Predefined radio stations in the iTunes library

I love internet radio. And I love iTunes. So the next logical step would be for me to manage my favorite radio stations in iTunes – preferably in a special playlist only so that the radio stations don’t clutter up my iTunes library.

Now, iTunes comes out-of-the-box with some predefined radio stations. You can simply drag your favorite radio stations to your playlist. However, iTunes’ radio station list is far from complete. So it would be nice to be able to add new radio stations to iTunes.

The first thing you need is the URL to the live stream of the new radio station. Unfortunately, there is no way to add this URL to iTunes’ “Radio” section. Although there is the menu item “Open Stream…” (in the “Advanced” menu) that let’s you open any live stream, this live stream would be added to your iTunes library. Why is this a bad thing? Well, you can’t edit the meta data (eg. genre, title, artist, …) for live streams. If you stop a live stream and then play it again, the meta data will be reset to whatever the live stream tells iTunes. So you’ll end up with a lot genres in your genre list you don’t want to have.

Drag .pls file to iTunes playlist

The alternative is to add the live stream just to a playlist without adding it to your library. This is possible. Simply drag the live stream’s playlist file (with .pls file ending) to your iTunes playlist. This will add all entries in the playlist file to your iTunes playlist without adding them to your iTunes library. That’s it.

If you don’t have a playlist file but only the live stream’s URL, you can create a playlist file quite easily. Simply open your favorite plain text editor (note that Word will not work) and copy the following text:

[playlist]
File1=http://streamexample.com:80
Title1=My Favorite Online Radio
Length1=-1

NumberOfEntries=1

Version=2

Replace the values of File1 and Title1 with your live stream’s URL and name respectively and save the file as radio.pls. Now you can drag it to your iTunes playlist and you’re done.

"Repeat one" in iTunes

Hint: You may want to activate “Repeat One” (in iTunes lower left corner) for this playlist. This prevents iTunes from going to the next radio station in the list when there is a problem with the one currently playing.