Question

I’m using this code to save bytes from a IntPtr buffer in unmanaged code to file. It’s a simple callback function:

private void callback(IntPtr buffer, int length)
{
    byte[] bytes = new byte[length];
    Marshal.Copy(buffer, bytes, 0, length);
    FileStream file = new FileStream(filename, FileMode.Create, FileAccess.Write);
    file.Write(bytes, 0, length);
    file.Close();
}

What I want is to store this data to file and throw it away. From what I understand there is a buffer in the unmanaged code and a 2nd one in MY code. I don’t want to copy the data around I want it directly:

// bad:     (unmanaged) buffer -> (managed) bytes -> file
// awesome: (unmanaged) buffer ->                    file

For my task I need the most quickest way to store the data to file.

Answer 1

Well, it’s called “managed” for some reason 🙂
What you can do though is declare WriteFile using P/Invoke, like this:

private void callback(IntPtr buffer, int length)
{
    FileStream file = new FileStream(filename, FileMode.Create, FileAccess.Write);
    int written;
    WriteFile(file.Handle, buffer, length, out written, IntPtr.Zero);
    file.Close();
}

 [DllImport("kernel32.dll")]
 private static extern bool WriteFile(IntPtr hFile, IntPtr lpBuffer, int NumberOfBytesToWrite, out int lpNumberOfBytesWritten, IntPtr lpOverlapped);