Question

I’m trying to pass an array of integers from c# to c++ via a managed memory file. Text was easy enough to get working, but I’m out of my depths in the c++ environment, and am not sure how to adjust this for an array of integers.

On the c# side, I pass:

pView = LS.Core.Platforms.Windows.Win32.MapViewOfFile(
                hMapFile,                       // Handle of the map object
                LS.Core.Platforms.Windows.Win32.FileMapAccess.FILE_MAP_ALL_ACCESS, // Read and write access
                0,                              // High-order DWORD of file offset 
                ViewOffset,                     // Low-order DWORD of file offset
                ViewSize                        // Byte# to map to the view
                );

byte[] bMessage2 = Encoding.Unicode.GetBytes(Message2 + '\0');
Marshal.Copy(bMessage2, 0, pView2, bMessage2.Length);

Here pView2 is the pointer to the memory mapped file.

On the c++ side, I call:

LPCWSTR pBuf;
pBuf = (LPCWSTR) MapViewOfFile(hMapFile, // handle to map object
           FILE_MAP_ALL_ACCESS,  // read/write permission
           0,
           0,
           BUF_SIZE);

How would I change this to handle an array of integers instead? Thanks!

Answer 1

a) You can copy the int[] into a byte[]. You can use BitConverter.GetBytes for this or bit arithmetic (byte0 = (byte)(i >> 24); byte1 = (byte)(i >> 16); …)

b) You can use unsafe code to bit-copy (blit) the int[] to the target byte[]

c) Maybe you can use Array.Copy. I think it can handle any blittable value type.

As per the comments I will elaborate on b):

int[] src = ...;
IntPtr target = ...;
var bytesToCopy = ...;

fixed(int* intPtr = src) {
 var srcPtr = (byte*)intPtr;
 var targetPtr = (byte*)target;
 for(int i from 0 to bytesToCopy) {
  targetPtr[i] = srcPtr[i];
 }
}