C# Signature:

[DllImport("kernel32.dll", CharSet=CharSet.Auto)]
static extern IntPtr FindFirstFile(string lpFileName, out WIN32_FIND_DATA lpFindFileData);

VB.NET Signature:

<DllImport("kernel32.dll", CharSet := CharSet.Auto)> _
Private Shared Function FindFirstFile(ByVal lpFileName As String, ByRef lpFindFileData As WIN32_FIND_DATA) As IntPtr
End Function

User-Defined Types:

WIN32_FIND_DATA

Notes:

The managed API only gives access to files/directories limited to 260 chars in length. This is a major flaw in the managed APIs, which every other administrator of a file server out there should agree on. This is the common scenario:

1. Create a folder like E:\CompanyData\Management on the server.

2. Share this as Management

3. The user mount this from his client PC to a drive letter like F:

4. The user creates directories and files below this F:. The user then has acess to a new 260 char length.

5. If the user creates a file with a name of e.g. 250 chars or with a combined length of subdirectorie names and file names of up to 260, these files will not be visible in Windows Explorer on the fileserver AND NOT be visible to the FileInfo DirectoryInfo, as well. in fact those API's blows up with an exception when encountering this situation.

Tips & Tricks:

Use CharSet=CharSet.Unicode, and prepend your filename to search for with "\\?\". This gives go access to filenames up to 32767 bytes in length.

Use "\\?\UNC\" prefix for fileshares.

Sample Code:

    public const int MAX_PATH = 260;
     public const int MAX_ALTERNATE = 14;

    [StructLayout(LayoutKind.Sequential)]
        public struct FILETIME {
        public uint dwLowDateTime;
        public uint dwHighDateTime;
     };

    [StructLayout(LayoutKind.Sequential, CharSet=CharSet.Unicode)]
    public struct WIN32_FIND_DATA {
        public FileAttributes dwFileAttributes;
        public FILETIME ftCreationTime;
        public FILETIME ftLastAccessTime;
        public FILETIME ftLastWriteTime;
        public int nFileSizeHigh;
        public int nFileSizeLow;
        public int dwReserved0;
        public int dwReserved1;
        [MarshalAs(UnmanagedType.ByValTStr, SizeConst=MAX_PATH)]
        public string cFileName;
        [MarshalAs(UnmanagedType.ByValTStr, SizeConst=MAX_ALTERNATE)]
        public string cAlternate;
    }

    [DllImport("kernel32", CharSet=CharSet.Unicode)]
    public static extern IntPtr FindFirstFile(string lpFileName, out WIN32_FIND_DATA lpFindFileData);

    [DllImport("kernel32", CharSet=CharSet.Unicode)]
    public static extern bool FindNextFile(IntPtr hFindFile, out WIN32_FIND_DATA lpFindFileData);

    private long RecurseDirectory(string directory, int level, out int files, out int folders) {
        IntPtr INVALID_HANDLE_VALUE = new IntPtr(-1);
        long size = 0;
        files = 0;
        folders = 0;
        Kernel32.WIN32_FIND_DATA findData;

        IntPtr findHandle;

        // please note that the following line won't work if you try this on a network folder, like \\Machine\C$
        // simply remove the \\?\ part in this case or use \\?\UNC\ prefix
        findHandle = Kernel32.FindFirstFile(@"\\?\" + directory + @"\*", out findData);
        if (findHandle != INVALID_HANDLE_VALUE) {

            do {
                if ((findData.dwFileAttributes & FileAttributes.Directory) != 0) {

                    if (findData.cFileName != "." && findData.cFileName != "..") {
                        folders++;

                        int subfiles, subfolders;
                        string subdirectory = directory + (directory.EndsWith(@"\") ? "" : @"\") +
                            findData.cFileName;
                        if (level != 0)  // allows -1 to do complete search.
                            {
                        size += RecurseDirectory(subdirectory, level - 1, out subfiles, out subfolders);

                        folders += subfolders;
                        files += subfiles;
                        }
                    }
                }
                else {
                    // File
                    files++;

                    size += (long)findData.nFileSizeLow + (long)findData.nFileSizeHigh * 4294967296;
                }
            }
            while (Kernel32.FindNextFile(findHandle, out findData));
            Kernel32.FindClose(findHandle);

        }

        return size;
    }

    // [Sample by Kåre Smith] // [Minor edits by Mike Liddell]

Alternative Managed API:

System.IO.Directory:

GetDirectories
GetFiles
GetFileSystemEntries

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