dynamic string formatting using string.format and List<T>.Count()

Question

I have to print out some PDFs for a project at work. Is there way to provide dynamic padding, IE. not using a code hard-coded in the format string. But instead based on the count of a List.

Ex.

If my list is 1000 elements long, I want to have this:

Part_0001_Filename.pdf... Part_1000_Filename.pdf

And if my list is say 500 elements long, I want to have this formatting:

Part_001_Filename.pdf... Part_500_Filename.PDF

The reason for this is how Windows orders file names. It sorts them alphabetically left-to-right or right-to-left, So I must use the leading zero, otherwise the ordering in the folder is messed up.

Solution

The simplest way is probably to build the format string dynamically too:

static List<string> FormatFileNames(List<string> files)
{
    int width = (files.Count+1).ToString("d").Length;

    string formatString = "Part_{0:D" + width + "}_{1}.pdf";

    List<string> result = new List<string>();

    for (int i=0; i < files.Count; i++)
    {
        result.Add(string.Format(formatString, i+1, files[i]));
    }
    return result;
}

This could be done slightly more simply with LINQ if you like:

static List<string> FormatFileNames(List<string> files)
{
    int width = (files.Count+1).ToString("d").Length;        
    string formatString = "Part_{0:D" + width + "}_{1}.pdf";

    return files.Select((file, index) => 
                            string.Format(formatString, index+1, file))
                .ToList();
}

Comments

[Chris]

@Jon: Thanks very much for your help. I used your LINQ implementation to store the format string for each file in the list I've created.