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?
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(typeof(byte)) * ar.Length);
Marshal.Copy(ar, 0, p, ar.Length);
Func(p);
Marshal.FreeHGlobal(p);
Marshal.SizeOf(object) does not work with arrays. I am pretty sure you will get an exception if you pass it an array but I do not have VS open in front of me right now to try. To correctly determine the size of an array, for your example the code would be Marshal.SizeOf(typeof(byte)) * ar.Length.
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) ;
