If you've done any programming at all, you'll probably have read a file line by line at some point. Fortunately, most libraries provide an easy way of doing that, and .Net is no exception: the TextReader.ReadLine method provides what you need. If you've used this method, you'll have written something like the following C# code.

using( StreamReader reader = File.OpenText("myfile.txt") )
{
    string line;
    while( (line = reader.ReadLine()) != null )
    {
        // Do something with the line
    }
}

While it does the job, personally I think it would be nicer and more semantic if we could use the foreach keyword for this. It's possible of course to use File.ReadAllLines for this purpose (we can use foreach to enumerate over the array it returns), but that reads the entire file into memory at once, so it's not a good solution if the file you want to read is big.

Fortunately, we can make it possible to do this with very little code indeed, thanks to extension methods (introduced in .Net 3.5) and the yield keyword (introduced in .Net 2.0).

public static class TextReaderExtensions
{
    public static IEnumerable<string> EnumerateLines(this TextReader reader)
    {
        if( reader == null )
            throw new ArgumentNullException("reader");

        string line;
        while( (line = reader.ReadLine()) != null )
        {
            yield return line;
        }
    }
}

Note that the extension is defined on TextReader, so you're not limited to using it with StreamReader; you can also use it with StringReader or anything else that inherits from TextReader.

With these few lines of code, we can now use foreach to enumerate over the lines of a file:

using( StreamReader reader = File.OpenText("myfile.txt") )
{
    foreach( string line in reader.EnumerateLines() )
    {
        // Do something with the line
    }
}

While this isn't much shorter than the original, it looks much nicer in my opinion.

Categories: Programming
Posted on: 2008-09-26 07:25 UTC. Show comments (3)

I am proud to announce a new utility here on Ookii.org: FormatC.

FormatC is a utility that allows you to add syntax highlighting to your C#, Visual Basic, C++, XML, HTML, Transact-SQL or PowerShell source code, so you can publish it on a web page or blog post.

Why does the world need yet another syntax highlighter? Mainly, because of none of the existing .Net based ones had the features I needed. That's right, FormatC is the utility I've been using to format source code for my own blog. So if you read my site you've already seen many examples, including this one which demonstrates one of those features I mentioned: Visual Basic XML literals. I dare say I'm one of the first to actually support that, although it does have some limitations (which are mentioned on the FormatC page). In fact, I have support for all C# 3.0 and Visual Basic 9.0 features, including Linq.

You can format your source code using the interface on my site and simply copy/paste the results into a webpage or blog post, and customize the highlighting by editing the provided style sheet (or simply keep the default). You can also download FormatC as a class library to use in your own application, or look at the source code. It's designed to be easily extensible, so you can add your own languages if you want.

If you use it, let me know what you think.

Categories: Software, General computing, Programming
Posted on: 2008-09-06 09:46 UTC. Show comments (3)