Patrick Bader's Blog a blog about software development

18Apr/111

Negating Booleans in C#

I was recently asked whether there is a short way to negate the value of a boolean variable. Surely you can simply asign the result of the negated variable to itself:

bool a;
[...]
a = !a;

So what is the problem here? Absolutely nothing of course. But now think of some common use case, for example in UI code:

MyForm.MyCheckbox.Checked = !MyForm.MyCheckbox.Checked;

Now, can you think of a way in C# to only write the variable name once?

There is indeed a way using compound assignment operators. The following code does the negation:

MyForm.MyCheckbox.Checked ^= true;

Well, I admit that this is not the clearest solution to the problem of negation, but it surely solves it. There is also an advantage or difference between this code and the initial. In the initial code "MyForm.MyCheckbox.Checked" will be evaluated twice and in the latter only once. Eric Lippert already wrote about this in his Blog.
Whether you will be using this obscure syntax or not is up to you. I for myself favour code where the intentions of the author are obvious which clearly is not the case here.

Tagged as: , 1 Comment
9Dec/100

foreach and lambdas in C#

I recently encountered a bug in a C# application I was writing and it took me quite a while to fix. The situation is as follows: I had an array with some kind of data I wanted to be processed by a thread pool. So my first approach was iterating over the array with a foreach loop and passing a lambda to the thread pool as argument. The code looked like this:

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object someState;
int items[] = {1, 2, 3, 4, 5};
 
foreach(int item in items)
{
	ThreadPool.QueueUserWorkItem((unused) => {
		System.Console.WriteLine(item);
	});
}

so, what's wrong with this code? Without the thread pool, nothing at all, it runs just fine, but with the thread pool the following text was written to the console:

5
5
5
5
5

When I saw the output, I was like: "what the hell is going wrong here?". The problem with the code above is: lambdas in C# capture their variables by-reference. For each iteration of the loop, a new value will be assigned to the item variable, an since this variable is captured by the lambda by-reference, all WorkItems in the thread pool will be influenced by the assignment of the loop. In my case the loop run completely, before the first WorkItem was executed. So the value of item was always the value which was last assigned by the loop.
A quick fix for this was assigning the loop variable to a local variable in the for loop:

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object someState;
int items[] = {1, 2, 3, 4, 5};
 
foreach(int item in items)
{
        int localItem = item;
	ThreadPool.QueueUserWorkItem((unused) => {
		System.Console.WriteLine(localItem);
	});
}

so, each lambda references its own local variable. Another solution is to pass the item explicitly to each WorkItem:

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object someState;
int items[] = {1, 2, 3, 4, 5};
 
foreach(int item in items)
{
	ThreadPool.QueueUserWorkItem((localItem) => {
		System.Console.WriteLine(localItem);
	},
        localItem);
}

The disadvantage here is: You have to make the variable explicitly available in the lambda, by passing it as a parameter.

Side note:
The upcoming C++0x release will also contain lambda expressions but it will allow you to specify whether a variable shall be bound by value or reference.

Filed under: C#, Uncategorized No Comments
23Jan/1024

Adjusting screen brightness with shortcuts

A while ago I installed Windows 7 on my Sony laptop. The good thing about it is it runs quite stable and most things just work. The bad thing some of the shortcuts with the blue "Fn" key don't work anymore. Adjusting the volume works perfectly fine, but setting the brightness of the LCD backlight does not.
Since Sony is not going to release any Windows 7 64 bit drivers for my model, I finally decided to write a little programm myself. This took several hours of searching for the right API to use. There are actualy three different ones:

  1. The first API I tried is called the Monitor Configuration of the Win32 API but did not work for my laptop (some kind of I2C transmission error occured)
  2. The Backlight Control Interface using IOCTL was the first approach that worked for me, but getting the current brightness is not supported on newer Windows versions
  3. So I ended up using WMI which is available for .NET and works surprisingly quite well.

Further usage information and a downloadable binary can be found on my Projects page
If you encounter bugs or have any suggestions please do not hesitate and give some feedback.

29Aug/090

… but how is it called in English?

English is not my mother tounge as you can surely guess. So I often have to translate some words from German to English and vica verse or look up words I don't know. I had a nice tool called Babylon Translator. It was just a trial version and ceased to work after the trial period. After living without a translation program for some years and having to look up words in online dictionaries I decided to write a translation program myself since I did not want to open my browser everytime I wanted to look up a word.
The result of a few C# programming hours was a little tool called Translator. At the moment it uses the dictionary at Leo.org to look up words maybe some more dictionaries will follow.
You can find the tool and source code here.

Have fun testing it and don't forget to give some feedback