PathCanonicalize equivalent in C#

quick and dirty:

In the past I have created a FileInfo object from the path string and then used the FullName property. This removes all of the ..\'s and the .\'s.

Of course you could interop:

 [DllImport("shlwapi", EntryPoint="PathCanonicalize")]
    private static extern bool PathCanonicalize(
        StringBuilder lpszDst,
        string lpszSrc
    );

3 solutions:

Best case scenario, where you are 100% certain the calling process will have full access to the filesystem. CAVEAT: permission on a production box can be tricky

    public static string PathCombineAndCanonicalize1(string path1, string path2)
    {
        string combined = Path.Combine(path1, path2);
        combined = Path.GetFullPath(combined);
        return combined;
    }

But, we're not always free. Often you need to do the string arithmetic without permission. There is a native call for this. CAVEAT: resorts to native call

    public static string PathCombineAndCanonicalize2(string path1, string path2)
    {
        string combined = Path.Combine(path1, path2);
        StringBuilder sb = new StringBuilder(Math.Max(260, 2 * combined.Length));
        PathCanonicalize(sb, combined);
        return sb.ToString();
    }

    [DllImport("shlwapi.dll", CharSet = CharSet.Auto, SetLastError = true)]
    private static extern bool PathCanonicalize([Out] StringBuilder dst, string src);

A third strategy is to trick the CLR. Path.GetFullPath() works just fine on a fictitious path, so just make sure you're always giving it one. What you can do is to swap out the root with a phony UNC path, call GetFullPath(), and then swap the real one back in. CAVEAT: this may require a hard sell in code review

    public static string PathCombineAndCanonicalize3(string path1, string path2)
    {
        string originalRoot = string.Empty;

        if (Path.IsPathRooted(path1))
        {
            originalRoot = Path.GetPathRoot(path1);
            path1 = path1.Substring(originalRoot.Length);
        }

        string fakeRoot = @"\\thiscantbe\real\";
        string combined = Path.Combine(fakeRoot, path1, path2);
        combined = Path.GetFullPath(combined);
        combined = combined.Substring(fakeRoot.Length);
        combined = Path.Combine(originalRoot, combined);
        return combined;
    }