Incremental Filenames

I was tinkering with a little program in C# this morning that needed to create incremental filenames instead of just overwriting the existing file.  As in: myfilename.htm -> myfilename_1.htm etc.

So here is the rough and ready version of what I did.

private string GetOutputFilename(string path,string filename,string extension)
{
     string[] files = Directory.GetFiles(path,filename+"*."+extension);
     if(files.Length==0) return path+"\\"+filename+"."+extension;
     return path+"\\"+filename+"_"+files.Length.ToString()+"."+extension;
}

It basically uses the filename+wildcard+extension to filter a directory listing.  If the listing is longer than zero it assumes that the next increment is going to be the number of files that are already there.

It’s a very simple algorithm that mostly works fine, but is not perfect.  Say you have the following files:

filename.htm
filename_1.htm
filename_2.htm
filename_3.htm

and you delete filename_2.htm.  This method will try to tell you that filename_3.htm is the next file – which is clearly wrong.