How can I pass a pointer to an array using p/invoke in C#?

Example C API signature:

void Func(unsigned char* bytes);

In C, when I want to pass a pointer to an array, I can do:

unsigned char* bytes = new unsigned char[1000];
Func(bytes); // call

How do I translate the above API to P/Invoke such that I can pass a pointer to C# byte array?

From stackoverflow

• You can use unsafe code:

  unsafe 
  {
       fixed(byte* pByte = byteArray)
       IntPtr intPtr = new IntPtr((void *) pByte);
       Func(intPtr);
  }
  

  If you need to use safe code, you can use a few tricks:

  IntPtr intPtr = Marshal.AllocHGlobal(Marshal.SizeOf(byteArray));
  Marshal.Copy(byteArray, 0, intPtr, Marshal.SizeOf(byteArray));
  
  Func(intPtr);
  
  Marshal.FreeHGlobal(intPtr);
  

  However, the safe code is going to be slow IMHO.

• Here is the appropriate signature for the native function.

  [System.Runtime.InteropServices.DllImportAttribute("<Unknown>", EntryPoint="Func")]
  public static extern  void Func(System.IntPtr bytes) ;
  

• The easiest way to pass an array of bytes is to declare the parameter in your import statement as a byte array.

  [DllImport EntryPoint="func" CharSet=CharSet.Auto, SetLastError=true]
  public extern static void Func(byte[]);
  
  byte[] ar = new byte[1000];
  Func(ar);
  

  You should also be able to declare the parameter as an IntPtr and Marshal the data manually.

  [DllImport EntryPoint="func" CharSet=CharSet.Auto, SetLastError=true]
  public extern static void Func(IntPtr p);
  
  byte[] ar = new byte[1000];
  IntPtr p = Marshal.AllocHGlobal(Marshal.SizeOf(ar));
  Marshal.Copy(ar, 0, p, ar.Length);
  Func(p);
  Marshal.FreeHGlobal(p);