I want to pass a byte[] to a method takes a IntPtr Parameter in C#, is that possible and how?
Another way,
GCHandle pinnedArray = GCHandle.Alloc(byteArray, GCHandleType.Pinned);
IntPtr pointer = pinnedArray.AddrOfPinnedObject();
// Do your stuff...
pinnedArray.Free();
The following should work but must be used within an unsafe context:
byte[] buffer = new byte[255];
fixed (byte* p = buffer)
{
IntPtr ptr = (IntPtr)p;
// Do your stuff here
}
Beware: you have to use the pointer within the fixed block. The GC can move the object once you are no longer within the fixed block.
Not sure about getting an IntPtr to an array, but you can copy the data for use with unmanaged code by using Mashal.Copy:
IntPtr unmanagedPointer = Marshal.AllocHGlobal(bytes.Length);
Marshal.Copy(bytes, 0, unmanagedPointer, bytes.Length);
// Call unmanaged code
Marshal.FreeHGlobal(unmanagedPointer);
Alternatively you could declare a struct with one property and then use Marshal.PtrToStructure, but that would still require allocating unmanaged memory.
Edit: Also, as Tyalis pointed out, you can also use fixed if unsafe code is an option for you
You could use Marshal.UnsafeAddrOfPinnedArrayElement to get a memory pointer to the array (or to a specific element in the array). Keep in mind that the array must be pinned first as per the API documentation:
The array must be pinned using a GCHandle before it is passed to this method. For maximum performance, this method does not validate the array passed to it; this can result in unexpected behavior.
Here's a twist on #user65157's answer (+1 for that, BTW):
I created an IDisposable wrapper for the pinned object:
class AutoPinner : IDisposable
{
GCHandle _pinnedArray;
public AutoPinner(Object obj)
{
_pinnedArray = GCHandle.Alloc(obj, GCHandleType.Pinned);
}
public static implicit operator IntPtr(AutoPinner ap)
{
return ap._pinnedArray.AddrOfPinnedObject();
}
public void Dispose()
{
_pinnedArray.Free();
}
}
then use it like thusly:
using (AutoPinner ap = new AutoPinner(MyManagedObject))
{
UnmanagedIntPtr = ap; // Use the operator to retrieve the IntPtr
//do your stuff
}
I found this to be a nice way of not forgetting to call Free() :)
Marshal.Copy works but is rather slow. Faster is to copy the bytes in a for loop. Even faster is to cast the byte array to a ulong array, copy as much ulong as fits in the byte array, then copy the possible remaining 7 bytes (the trail that is not 8 bytes aligned). Fastest is to pin the byte array in a fixed statement as proposed above in Tyalis' answer.
In some cases you can use an Int32 type (or Int64) in case of the IntPtr. If you can, another useful class is BitConverter. For what you want you could use BitConverter.ToInt32 for example.
Related
I need to slice a byte[] and pass the sliced section to a C# DLL for processing. I am avoiding Array.Copy, because I am trying not to copy anything to hinder performance. I have been made aware of the ArraySegment class as well as Span and Memory. The confusion I am having is how to actually pass these to the DLL, as I am passing an UnmanagedType.LPArray like so:
[UnmanagedFunctionPointer(CallingConvention.StdCall)]
public delegate int ProcessVideoFrame_t([MarshalAs(UnmanagedType.LPArray)] byte[] bytes, uint len);
Is there any way to get an underlying byte[] from these classes, or somehow pass the segment without making a copy?
My current code is:
byte[] bytes = new byte[packet.Payload.Length - headerSize];
Array.Copy(packet.Payload, headerSize, bytes, 0, bytes.Length);
helper.ProcessVideoFrame(CookieHelperDictionary[packet.Header.Cookie], bytes, (uint)bytes.Length);```
unsafe
{
fixed (byte* p = &packet.Payload[headerSize])
{
helper.ProcessVideoFrame(CookieHelperDictionary[packet.Header.Cookie], (IntPtr)p, (uint)(packet.Payload.Length - headerSize));
}
}
I also changed the function definition to this:
[UnmanagedFunctionPointer(CallingConvention.StdCall)]
public delegate int ProcessVideoFrame_t(IntPtr rdh, IntPtr buffer, uint len);
I'm trying to fill a structure (does not have to be an actual struct), with data loaded from a byte[].
There are many different data structures in the byte[], one of them is a string, which is declared as:
UInt16 stringLenght
byte[stringLenght] zeroTerminatedString
I 'c' language this could be handled by declaring a fixed size struct, and instead of a the struct containing the actual string, make a pointer to the string.
Something like:
UInt16 stringLength
char* zeroTerminatedString
Is there a (smart) way to do something similar in c#? I mean loading binary data from a file/memory and filling it into a structure?
Regards
Jakob Justesen
That's not how you'd declare it in C. If the record in the file contains a string then you'd declare the structure similar to:
struct Example {
int mumble; // Anything, not necessarily a string length
char text[42];
// etc...
};
The equivalent C# declaration would look like:
[StructLayout(LayoutKind.Sequential, Pack = 1, CharSet = CharSet.Ansi)]
private struct Example {
public int mumble;
[MarshalAs(UnmanagedType.ByValTStr, SizeConst = 42)]
public string text;
// etc...
}
You'd normally use BinaryReader to read the data. But it cannot handle strings like this directly, you have to read them as a byte[] and do the string conversion yourself. You also cannot take advantage of the declarative syntax, you have to write a call for each individual member of the struct.
There's a workaround for that, the Marshal class already knows how to convert unmanaged structures to managed ones with the PtrToStructure() method. Here's a generic implementation, it works for any blittable type. Two versions, a static one that reads from a byte[] and an instance method that was optimized to repeatedly read from a stream. You'd use a FileStream or MemoryStream with that one.
using System;
using System.IO;
using System.Runtime.InteropServices;
class StructTranslator {
public static bool Read<T>(byte[] buffer, int index, ref T retval) {
if (index == buffer.Length) return false;
int size = Marshal.SizeOf(typeof(T));
if (index + size > buffer.Length) throw new IndexOutOfRangeException();
var handle = GCHandle.Alloc(buffer, GCHandleType.Pinned);
try {
IntPtr addr = (IntPtr)((long)handle.AddrOfPinnedObject() + index);
retval = (T)Marshal.PtrToStructure(addr, typeof(T));
}
finally {
handle.Free();
}
return true;
}
public bool Read<T>(Stream stream, ref T retval) {
int size = Marshal.SizeOf(typeof(T));
if (buffer == null || size > buffer.Length) buffer = new byte[size];
int len = stream.Read(buffer, 0, size);
if (len == 0) return false;
if (len != size) throw new EndOfStreamException();
var handle = GCHandle.Alloc(buffer, GCHandleType.Pinned);
try {
retval = (T)Marshal.PtrToStructure(handle.AddrOfPinnedObject(), typeof(T));
}
finally {
handle.Free();
}
return true;
}
private byte[] buffer;
}
Untested, hope it works.
The Marshal should be able to do this for you.
Note that this can only be done to a struct and you will probably need to use the StructLayout attribute.
I'm not 100% sure on how to handle the string or arrays, but BStrWrapper or ArrayWithOffset MIGHT help, also keep on the lookout for similar classes/attributes (I know I have done stuff like this before for binding to native functions).
I am using the excellent VLC wrapper created by Roman Ginzburg re: nVLC
This part of his code returns a bitmap object.
In myh calling code I then convert it to a byte array.
I sthere a way to directly convert the memory pointer to a byte array with converting to a bitmap object.
this is his code:
unsafe void OnpDisplay(void* opaque, void* picture)
{
lock (m_lock)
{
PixelData* px = (PixelData*)opaque;
MemoryHeap.CopyMemory(m_pBuffer, px->pPixelData, px->size);
m_frameRate++;
if (m_callback != null)
{
using (Bitmap frame = GetBitmap())
{
m_callback(frame);
}
}
}
}
private Bitmap GetBitmap()
{
return new Bitmap(m_format.Width, m_format.Height, m_format.Pitch, m_format.PixelFormat, new IntPtr(m_pBuffer));
}
What I would like is another function like:
private byte[] GetBytes()
{
//not sure what to put here...
}
I am lookinga s I type but still cannot find anything or even if it possible to do so...
Thanks
Use Marshal.Copy. Like this:
private byte[] GetBytes() {
byte[] bytes = new byte[size];
Marshal.Copy(m_pBuffer, bytes, 0, size);
return bytes;
}
I'm not quite sure where you are storing the size of the buffer, but you must know that.
An aside. Why do you write new IntPtr(m_pBuffer) in GetBitmap rather than plain m_pBuffer?
I also wonder why you feel the need to use unsafe code here. Is it really needed?
As a follow-up to my previous question, I finally got the C dll exported and usable in C#, but I'm stuck trying to figure out the proper argument types and calling method.
I've researched here on SO but there doesn't seem to be a pattern to how variable types are assigned.
I see some people suggest a StringBuilder for uchar*, others a byte[], some references to 'unsafe' code, etc. Can anyone recommend a solution based on this specific use-case?
Also note the exception generated as the code stands now, right after the call to the C function.
C function import:
[DllImport("LZFuncs.dll")]
internal static extern long LZDecomp(ref IntPtr outputBuffer, byte[] compressedBuffer, UInt32 compBufferLength); //Originally two uchar*, return is size of uncompressed data.
C function signature:
long LZDecomp(unsigned char *OutputBuffer, unsigned char *CompressedBuffer, unsigned long CompBufferLength)
Used as below:
for (int dataNum = 0; dataNum < _numEntries; dataNum++)
{
br.BaseStream.Position = _dataSizes[dataNum]; //Return to start of data.
if (_compressedFlags[dataNum] == 1)
{
_uncompressedSize = br.ReadInt32();
byte[] compData = br.ReadBytes(_dataSizes[dataNum] - 4);
IntPtr outData = IntPtr.Zero;
LZFuncs.LZDecomp(ref outData, compData, Convert.ToUInt32(compData.Length));
var uncompData = new byte[_uncompressedSize]; //System.ExecutionEngineException was unhandled
Marshal.Copy(outData, uncompData, 0, Convert.ToInt32(_uncompressedSize));
BinaryWriter bw = new BinaryWriter(new FileStream("compData" + dataNum + ".txt", FileMode.CreateNew));
bw.Write(uncompData);
bw.Close();
}
else
{
BinaryWriter bw = new BinaryWriter(new FileStream("uncompData" + dataNum + ".txt", FileMode.CreateNew));
bw.Write(br.ReadBytes(_dataSizes[dataNum]));
bw.Close();
}
}
I assume the C code is clobbering the memory pretty severely if it's breaking the C# caller with a CLR exception like that, but due to how the C code is written, there's absolutely no way to modify it without breaking the functionality, it's effectively a black box. (Written in assembly, for the most part.)
For reference, just a few questions I've read over in an effort to solve this myself:
How do I return a byte array from C++ to C#
Correct way to marshall uchar[] from native dll to byte[] in c#
There have been others but those are the most recent.
OK, that's not too hard to work with. The two buffer parameters are byte arrays. You should declare them as byte[]. The calling convention is Cdecl. Remember that C++ long is only 32 bits wide on Windows, so use C# int rather than C# long since the latter is 64 bits wide.
Declare the function like this:
[DllImport("LZFuncs.dll", CallingConvention = CallingConvention.Cdecl)]
internal static extern int LZDecomp(
[Out] byte[] outputBuffer,
[In] byte[] compressedBuffer,
uint compBufferLength
);
You are decompressing compressedBuffer into outputBuffer. You'll need to know how large outputBuffer needs to be (the code in the question shows that you already handle this) and allocate a sufficiently large array. Beyond that I think it's obvious how to call this.
The calling code will this look like this:
_uncompressedSize = br.ReadInt32();
byte[] compData = br.ReadBytes(_dataSizes[dataNum] - 4);
byte[] outData = new byte[_uncompressedSize];
int len = LZFuncs.LZDecomp(outData, compData, (uint)compData.Length);
This is an old question but a real issue and can lead to serious security issues so I thought I give it my 2 cents
Whenever I use [DllImport] I always add the location you consider safe, one option is to specify is for windows DLL's
[DefaultDllImportSearchPaths(DllImportSearchPath.SafeDirectories)]
However, have a look at your options to have it match your needs, you might load a private DLL that is located elsewhere.
I have a function that want to receive sbyte* buffer how to create such in C# from scratch and from existing byte[]?
// Allocate a new buffer (skip this if you already have one)
byte[] buffer = new byte[256];
unsafe
{
// The "fixed" statement tells the runtime to keep the array in the same
// place in memory (relocating it would make the pointer invalid)
fixed (byte* ptr_byte = &buffer[0])
{
// Cast the pointer to sbyte*
sbyte* ptr_sbyte = (sbyte*) ptr_byte;
// Do your stuff here
}
// The end of the "fixed" block tells the runtime that the original array
// is available for relocation and/or garbage collection again
}
Casting to Array and then casting to byte[] will be enough.
byte[] unsigned = { 0, 1, 2 };
sbyte[] signed = (sbyte[]) (Array)unsigned;