Develop Reference

PInvoke Array Marshalling Failure

I have the following C++ function exported in a DLL:
extern "C" __declspec(dllexport) bool GetResolutionArray(int32_t adapterIndex, int32_t outputIndex, uint32_t arrayLength, Resolution outResolutionArr[]) {
memcpy_s(
outResolutionArr,
sizeof(Resolution) * arrayLength,
RENDER_COMPONENT.GetResolutionArray(adapterIndex, outputIndex),
RENDER_COMPONENT.GetOutput(adapterIndex, outputIndex).NumResolutions * sizeof(Resolution)
);
return true;
}
And, the matching extern function declaration in C#:
[DllImport(InteropUtils.RUNTIME_DLL, EntryPoint = "GetResolutionArray", CallingConvention = CallingConvention.Cdecl)]
internal static extern bool _GetResolutionArray(int adapterIndex, int outputIndex, uint resolutionArrayLength, [MarshalAs(UnmanagedType.LPArray), In, Out] ref Resolution[] resolutions);
However, when I attempt to use this function as below, the program crashes with a FatalExecutionEngineError (indicating I corrupted something somewhere I guess) (error code 0xc0000005, i.e. access violation):
Resolution[] resolutions = new Resolution[outOutputDesc.NumResolutions];
if (!_GetResolutionArray(outAdapterDesc.AdapterIndex, outOutputDesc.OutputIndex, (uint) resolutions.Length, ref resolutions)) {
EnginePipeline.TerminateWithError("Internal engine call failed: _GetResolutionArray");
}
I strongly suspect that my call to memcpy_s is causing the access violation, but I can't see how or why, and I therefore reason that perhaps the marshalling is going wrong somewhere.
Thank you.

The array parameter is declared incorrectly. A C# array is already a reference and so you don't need the ref. Declare it like this:
[DllImport(InteropUtils.RUNTIME_DLL, EntryPoint = "GetResolutionArray",
CallingConvention = CallingConvention.Cdecl)]
internal static extern bool _GetResolutionArray(int adapterIndex,
int outputIndex, uint resolutionArrayLength, Resolution[] resolutions);

Trouble with DllImport syntax calling GetJob() from a printer driver library

I'm trying to call the GetJob() method documented here. I think I'm having problems with the syntax of the routine right now, both calling and defining. I've finally got something to compile which is the following.
[DllImport(
"winspool.drv",
EntryPoint = "GetJob",
SetLastError = true,
CharSet = CharSet.Ansi,
ExactSpelling = true,
CallingConvention = CallingConvention.StdCall)]
private static extern bool GetJob
([InAttribute()] IntPtr hPrinter,
[InAttribute()] Int32 JobId,
[InAttribute()] Int32 Level,
[OutAttribute()] out byte[] pJob,
[InAttribute()] Int32 cbBuf,
[OutAttribute()] out Int32 pcbNeeded);
...
...
...
...
const int BUFFER_SIZE = 250;
int pcbNeeed = 0;
unsafe
{
byte[] byteBuffer = new byte[BUFFER_SIZE];
bResult = GetJob(m_PrinterHandle, jobID, 1, out byteBuffer, BUFFER_SIZE, out pcbNeeed);
}
According to the documentation here, it seems I should be able to use a byte[] without any special marshaling code because it is "blittable". In anycase, I get a runtime exception that says:
Unable to find an entry point named 'GetJob' in DLL 'winspool.drv'.
at NQBB.Printer.PrintQueueMonitor.PrinterWatcher.GetJob(IntPtr hPrinter, Int32 JobId, Int32 Level, Byte[]& pJob, Int32 cbBuf, Int32& pcbNeeded)
I think I just have some syntax wrong here. Can anyone see the problem?

Stop using ExactSpelling and then you will link to GetJobA or GetJobW as appropriate.

Try setting EntryPoint to "GetJobA". GetJob is not actually in the winspool export list...

A Problem in Pinvoke

I have the following function in C++ native dll, and I want to use it in a C# app.
DWORD __cdecl Foo(
LPCTSTR Input,
TCHAR** Output,
DWORD Options,
ErroneousWord** List = NULL,
LPDWORD Count = 0
);
Using Pinvoke
[DllImport("dllName", CharSet = CharSet.Unicode, CallingConvention = CallingConvention.Cdecl)]
public static extern UInt32 Foo(string InputWord, out string Output, UInt32 Options, out object List,out UInt32 Count);
Calling code:
string output;
object dummyError = null;
uint dummyCount = 0;
uint x = 0;
Foo(Text, out output, x | y,out dummyError,out dummyCount);
I got the following exception
Attempted to read or write protected
memory. This is often an indication
that other memory is corrupt
P.S:
ErroneousWord is struct and I do not need its output, so I marshal it as object

That error more than likely means that you have a marshaling problem.
You don't show us what the ErroneousWord type is, but I assume it's some kind of class defined in your C++ code. My guess is that it's not being marshaled correctly to a .NET object.
Considering that it's a pointer (or a pointer to a pointer), try changing that parameter to an IntPtr type to represent a pointer, instead. It shouldn't matter, since you're simply passing NULL for the argument anyway, easily represented using the static IntPtr.Zero field.
You probably also want to marshal Output the exact same way. If you change the parameter to an IntPtr type, you'll receive a pointer to a TCHAR*, which you can then pass to the other unmanaged functions however you see fit (e.g., to free it).
Try the following code:
[
DllImport("dllName",
CharSet = CharSet.Unicode,
CallingConvention = CallingConvention.Cdecl)
]
public static extern UInt32 Foo(
string InputWord,
out IntPtr Output, // change to IntPtr
UInt32 Options,
out IntPtr List, // change to IntPtr
out UInt32 Count);
IntPtr output;
IntPtr dummyError = IntPtr.Zero;
uint dummyCount = 0;
uint x = 0;
Foo(Text, out output, x | y, out dummyError, out dummyCount);
You might also need to use the Marshal.AllocHGlobal method to allocate unmanaged memory from your process that is accessible to the C++ code. Make sure that if you do so, you also call the corresponding Marshal.FreeHGlobal method to release the memory.

Given Cody's answer and the comments, you will have to do it this way:
[DllImport("dllName", CharSet = CharSet.Unicode, CallingConvention = CallingConvention.Cdecl)]
extern static UInt32 Foo(string InputWord, out IntPtr Output, UInt32 Options, out IntPtr List, out UInt32 Count);
Now to get the string value in Output marshalled over to managed memory you will do:
string outputValue = Marshal.PtrToStringAnsi(Output);
You must know if TCHAR is Ansi or Unicode and use the appropriate marshal.
Remember to hang onto the Output IntPtr so you can pass that to the native Free method.

Thanks Cody for your answer but I want to make a seperate one, first Output is created by Foo from the native side, and I call FreeFoo to free the allocated memory by Foo.
The following is the code
[DllImport("dllname", CharSet = CharSet.Unicode, CallingConvention = CallingConvention.Cdecl)]
public static extern UInt32 Correct(string InputWord, out IntPtr Output, UInt32 Options, out object List,out UInt32 Count);
[DllImport("dllname", CharSet = CharSet.Unicode, CallingConvention = CallingConvention.Cdecl)]
public static extern void FreeFoo(IntPtr Output);
}
To use it:
public string FooWrapper(string Text)
{
IntPtr output;
object dummyError = null;
uint dummyCount = 0;
uint x = 0;
Foo(Text, out output, x,out dummyError,out dummyCount);
string str = Marshal.PtrToStringUni(output);
FreeFoo(output);
return str;
}

Whatever the ErroneousWord type is, you can't marshal an array as a single out object. If it is at all possible to marshal as an object...

Wrapper c# using unmanaged dll

I am making a wrapper to read TDM and TDMS files but i have a problem
[DllImport(lib, CharSet = CharSet.Auto)]
static extern int DDC_OpenFileEx(
[MarshalAs(UnmanagedType.LPStr)]
string filePath,
[MarshalAs(UnmanagedType.LPStr)]
string fileType,
int read_only,
ref long file);
works fine but
[DllImport(lib, CharSet = CharSet.Auto, SetLastError = true)]
static extern int DDC_GetNumChannelGroups(long file,
[MarshalAs(UnmanagedType.U4)]
ref int numChannelGroups);
int numGru = 0;
errCode = ReadTDM.DDC_GetNumChannelGroups(file,ref numGru);
System.Console.WriteLine("Error Code {0} GetNumChannelGroups", errCode);
gives an error -6202, // An invalid argument was passed to the library.
i have tried ref uint, uint * (unsafe), UIntPtr. The def from .h file
int __stdcall DDC_GetNumChannelGroups (DDCFileHandle file,unsigned int *numChannelGroups);
the second parametr is the problem.
it seems that unsigned int* != uint.
Does anyone have an idea how to call this function form the dll?
http://forums.ni.com/ni/board/message?board.id=60&thread.id=11821

It is the 1st argument that's declared wrong. That throws off the stack frame and prevents the unmanaged code from properly reading the pointer for the 2nd argument. "long" is 64-bits, DDCFileHandle is almost certainly a pointer, 32-bits on a 32-bit operating system.
Change the argument declaration to IntPtr. You'll also need to change the declaration of the function that returns that handle.

C++ function calling from C# application. Attempted to read or write protected memory

The problem below is ralated to my previous question
Converting static link library to dynamic dll
My first step was to develop a dll, that was done. (Thanks John Knoeller prakash. Your input was very helpful)
Now when i call the function in the dll from my c# application i get the error
"Attempted to read or write protected memory. This is often an indication that other memory is corrupt."
Here is the C++ definition
extern "C" DEMO2_API void Decompress(char* inp_buff, unsigned short*
inp_len, char* buffer_decomp,unsigned *output_len,unsigned short* errorCode);
My C# Converstion p/Involke
private static extern void Decompress(
byte[] inp_buff,
ref ushort inp_len,
byte[] buffer_decomp,
ref int output_len,
ref ushort errorCode
);
And I am calling it as below
byte[] dst = new byte[2048];
int outlen = 2048;
ushort errorCode = 0;
Decompress(src, (ushort )src.Length, dst, ref outlen,ref errorCode);
return dst;
What is wrong?

I see a signature mismatch on the inp_len parameter. In the C++ definition you use a pointer to a short unsigned int, while in the C# method you use a ushort.

for pointers you must use IntPtr .net type

#necrostaz
It is not necessary that we use IntPtr for pointers.
Look below all of these four declarations are valid and currently i am using it.
[DllImport("user32.dll")]
public static extern IntPtr SendMessage(IntPtr hWnd, int msg, int wParam, String lParam);
[DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = false)]
public static extern IntPtr SendMessage(IntPtr hWnd, Int32 Msg, IntPtr wParam, IntPtr lParam);
[DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = false)]
public static extern IntPtr SendMessage(IntPtr hWnd, Int32 Msg, IntPtr wParam, StringBuilder lParam);
[DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = false)]
public static extern IntPtr SendMessage(IntPtr hWnd, Int32 Msg, IntPtr wParam, String lParam);
question is still open

In addition to the missing "ref" on the inp_len declaration that Maurits pointed out, you need to make sure that your pointer sizes match.
If you're running on a 32-bit operating system you should be OK, but if your code runs on 64-bit too, then you need to ensure that either:
You mark your .net entry assembly as x86 (not Any CPU)
or
You supply a 32-bit and 64-bit build of the C++ dll and install the correct one for the interop to call.

I have had the same problem two years ago. In my case the reason for the access violation was that the memory was allocated outside the DLL. As a solution I added two functions for memory allocation and deallocation to the DLL.
Another solution could be a change of the .net security settings. Some keywords are "Code Access Security Police Tool" (caspol.exe) and ".NET Framework Configuration Tool" (mscorcfg.msc). In VS there is also a security tab in the project property dialog. I'm not an expert in .net security so someone else should know more details.

The following code runs without any problems. It's very similar to yours:
C++:
extern "C" __declspec(dllexport) void TestFunction(char* inp_buff,
unsigned short* inp_len,
char* buffer_decomp,
unsigned *output_len,
unsigned short* errorCode)
{
//copy input buffer to output buffer
int size = min(*inp_len,*output_len);
for(int i=0; i<size; i++)
buffer_decomp[i] = inp_buff[i];
errorCode = 0;
}
C#:
using System;
using System.Runtime.InteropServices;
class Program
{
[DllImport("TEST.DLL")]
public static extern void TestFunction(byte[] inp_buff,
ref ushort inp_len,
byte[] out_buff,
ref int out_len,
ref ushort errorCode);
static void Main(string[] args)
{
//prepare input buffer
byte[] inp_buff = new byte[20];
inp_buff[0] = (byte)'T';
inp_buff[1] = (byte)'E';
inp_buff[2] = (byte)'S';
inp_buff[3] = (byte)'T';
ushort inp_len = (ushort)inp_buff.Length;
//prepare output buffer
byte[] out_buff = new byte[20];
int out_len = out_buff.Length;
ushort errorCode = 0;
TestFunction(inp_buff, ref inp_len, out_buff, ref out_len, ref errorCode);
//see if copying was successful
for(int i=0; i<out_len; i++)
Console.Out.Write(out_buff[i]);
}
}
Try it out. I have taken a look at the open parts of the library you are using. Here is a direct excerpt of the function lzo_decomp:
in = lzo_malloc(IN_LEN);
out = lzo_malloc(OUT_LEN);
wrkmem = lzo_malloc(LZO1Z_999_MEM_COMPRESS);
if (in == NULL || out == NULL || wrkmem == NULL)
{
printf("out of memory\n");
}
in_len = IN_LEN;
lzo_memset(in,0,in_len );
lzo_memset ( out, 0, OUT_LEN );
memcpy ( out, &input_buffer, inp_buff_len);
lzo_free(wrkmem);
lzo_free(out);
lzo_free(in);
r = lzo1z_decompress(out,*inp_len,in,&out_len,NULL );
For serenity: "in" and "out" are not the function arguments for the input and output buffers but temporary pointers. What can you see (beside from bad formatted code)? The only two buffers lzo1z_decompress is called with are "in" and "out". And these two buffers are freed before the call. I'm not surprised that there is an access violation. I only can underline nobugz's advice: Contact the author.

The 4th parameter need to be passed using out mode instead of ref. That solved the problem.