How to store values persistenly of files in a directory?

Question

I\'m developing a Windows application in VS2005 using C#. In my project, I generate dlls and store them in a directory. The dlls will be named as TestAssembly1, TestAssembly

Answer 1

Personally I'd use a binary search to find the next assembly...

• start n=1
• does TestAssembly1.dll exist? (yes)
• does TestAssembly2.dll exist? (yes)
• does TestAssembly4.dll exist? (yes)
• does TestAssembly8.dll exist? (yes)
• does TestAssembly16.dll exist? (yes)
• does TestAssembly32.dll exist? (no)

and no use binary search between 16 and 32:

• does TestAssembly24.dll exist? (yes)
• does TestAssembly28.dll exist? (yes)
• does TestAssembly30.dll exist? (no)
• does TestAssembly29.dll exist? (yes)

so use TestAssembly30.dll

This avoids the need to keep the count separately, so it'll work even if you delete all the files - and the binary search means you don't have too bad performance.

Untested, but something like below; also note that anything based on file existence is immediately a race condition (although usually a very slim one):

    static string GetNextFilename(string pattern) {
        string tmp = string.Format(pattern, 1);
        if (tmp == pattern) {
            throw new ArgumentException(
                 "The pattern must include an index place-holder", "pattern");
        }
        if (!File.Exists(tmp)) return tmp; // short-circuit if no matches

        int min = 1, max = 2; // min is inclusive, max is exclusive/untested
        while (File.Exists(string.Format(pattern, max))) {
            min = max;
            max *= 2;
        }

        while (max != min + 1) {
            int pivot = (max + min) / 2;
            if (File.Exists(string.Format(pattern, pivot))) {
                min = pivot;
            }
            else {
                max = pivot;
            }
        }
        return string.Format(pattern, max);
    }