Question

I’m trying to use a method from a C++ DLL in a C# project, but I’m, having problems calling it correctly.
The method is this:

As said in the SDK manual

DWORD WINAPI PrtRead (HANDLE hPrt, DWORD dwTimeout, DWORD *pdwType, LPDWORD pdwParArray, LPDWORD pdwArraySize, LPBYTE pbReadData, LPDWORD pdwReadDataLen)

As really defined on code

extern "C" __declspec(dllimport) DWORD PrtRead (HANDLE hPRT, DWORD dwTimeout, DWORD *pdwType, LPDWORD pdwParArray, LPDWORD pdwArraySize,LPBYTE  pbReadData, LPDWORD pdwReadDataLen);

and in the SDK C++ sample they call it like this:

DWORD       dwPar[2];
pdwParArray = &dwPar[0];
dwPar[0] = 0;
dwPar[1] = 0;

DWORD dwRet = PrtRead(hPrinter, dwCurrentTimeout, &dwType, pdwParArray, &dwArraySize, NULL, &dwReadDataLen);

My problem is getting the value LPDWORD pdwParArray.

The DLL always returns one of the following values in position [0]: 1, 2 or 20 and in postion [1]: 1, 2 or 4, but I’m unbale to make it do this.

I’ve tryed defining the import like this:

[DllImport("HPRDH.dll", CallingConvention = CallingConvention.Cdecl)]
public static extern ulong PrtRead(IntPtr hPrt, ulong dwTimeout, ref ulong pdwType, XXXXXXXXX , ref ulong pdwArraySize, ref byte[] pbReadData, ref ulong pdwReadDataLen);

and varied XXXXXXXXX like this

---

Method definition:

out ulong[] pdwParArray

Variable Initialization:

ulong[] pdwParArray;

Method returns:

pdwParArray = null

---

Method definition:

ref ulong[] pdwParArray

Variable Initialization:

ulong[] pdwParArray = new ulong[2];
pdwParArray[0] = 0;
pdwParArray[1] = 0;

Method returns:
pdwParArray[0] = 0;
pdwParArray[1] = Out of bounds array index;

---

Method definition:
out ulong pdwParArray

Variable Initialization:
ulong[] pdwParArray = new ulong[2];

Method returns:
pdwParArray[0] = 0;
pdwParArray[1] = 0;

---

Method definition:
ref ulong pdwParArray

Variable Initialization:
ulong[] pdwParArray = new ulong[2];

Method returns:
pdwParArray[0] = 0;
pdwParArray[1] = 0;

---

How should I define the LPDWORD pdwParArray in my C# import, how to initialize it and call it?

Thanks in advance

_
_
_
_

EDIT:
@TheMathemagician

Tried the following with these results:

Definition:

[MarshalAs(UnManagedType.LPArray)] ulong[] pdwParArray

Result:

pdwParArray[0] = 0;

pdwParArray[1] = 0;

---

Definition:

[MarshalAs(UnmanagedType.LPArray)] out ulong[] pdwParArray

Result:

pdwParArray[0] = null;

pdwParArray[1] = null;

---

Definition:

[MarshalAs(UnmanagedType.LPArray)] ulong pdwParArray

Result:

Cannot marshal ‘parameter #4’: Invalid managed/unmanaged type combination (Int64/UInt64 must be paired with I8 or U8).

---

Definition:

[MarshalAs(UnmaDefinition:nagedType.LPArray)] out ulong pdwParArray

Result:

Cannot marshal ‘parameter #4’: Invalid managed/unmanaged type combination (Int64/UInt64 must be paired with I8 or U8).

Answer 1

As almost all the answers where about the same thing, and even so It wasn’t working, I decided to look even deeper into the SDK sample, and realized I needed to call PrtRead(…) a second time to get the correct values.

I ended up by using:

[DllImport("HPRDH.dll", CallingConvention = CallingConvention.Cdecl)]
public static extern UInt32 PrtRead(IntPtr hPrt, UInt32 dwTimeout, ref UInt32 pdwType, out UInt32 pdwParArray, ref UInt32 pdwArraySize, ref byte[] pbReadData, ref UInt32 pdwReadDataLen);