ERROR_MORE_DATA — PVOID and C# — Unmanaged types

Question

How can I get the value from the following DLL? offreg.dll.

In my below code, I have successfully opened the hive, the key and now I am trying to get the value of the key and I keep running into the ERROR_MORE_DATA (234) error.

Here is the C++ .dll:

DWORD
ORAPI
ORGetValue (
    __in ORHKEY     Handle,
    __in_opt PCWSTR lpSubKey,
    __in_opt PCWSTR lpValue,
    __out_opt PDWORD pdwType,
    __out_bcount_opt(*pcbData) PVOID pvData,
    __inout_opt PDWORD pcbData
    );

Here is my C# code:

        [DllImport("offreg.dll", CharSet = CharSet.Auto, EntryPoint = "ORGetValue", SetLastError = true, CallingConvention = CallingConvention.StdCall)]
        public static extern uint ORGetValue(IntPtr Handle, string lpSubKey, string lpValue, out uint pdwType, out StringBuilder pvData, out uint pcbData);

            IntPtr myHive;            
            IntPtr myKey;
            StringBuilder myValue = new StringBuilder("", 256);
            uint pdwtype;
            uint pcbdata;

 uint ret3 = ORGetValue(myKey, "", "DefaultUserName", out pdwtype, out myValue, out pcbdata);

So the issue seems to be around PVOID pvData I can't seem to get the right type, or buffer size right. Always with the 234 error.

NOTE: When running this command pcbdata = 28... so 256 should be more than enough.

Any help would be greatly appreciated.

As shown above, I've tried string builder... string... IntPtr... etc. None of which were able to handle the out of PVData...

Thank you.

Answer 1

You need to initialize pcbData to the size of your buffer before passing it in. Remember C doesn't know how large of a buffer you are passing it, the pcbData value coming in tells the function how large pvData is. In your case you are passing in zero, telling OrGetValue that you that pvData is a 0 byte buffer, so it responds telling you it needs a larger buffer.

So in your PInvoke definiation pcbData should be a ref param and have a non-zero value going in:

[DllImport("offreg.dll", CharSet = CharSet.Auto, EntryPoint = "ORGetValue", SetLastError = true, CallingConvention = CallingConvention.StdCall)]
public static extern uint ORGetValue(IntPtr Handle, string lpSubKey, string lpValue, out uint pdwType, out StringBuilder pvData, ref uint pcbData);

IntPtr myHive;            
IntPtr myKey;
StringBuilder myValue = new StringBuilder("", 256);
uint pdwtype;
uint pcbdata = myValue.Capacity();

uint ret3 = ORGetValue(myKey, "", "DefaultUserName", out pdwtype, out myValue, ref pcbdata);