PInvoke - Issue while calling DJVU function from C# Code - Attempted to read or write protected memory

Question

Hi,
I know there are many questions in this subject but none of them help to resolve the issue I am currently facing.
Below is the signature of C Function from DJVULibre added in .NET code
[DllImport("C:\\Program Files\\DJVULIBRE\\LIBDJVULIBRE.dll", CharSet=CharSet.Ansi, CallingConvention = CallingConvention.Cdecl)]
private unsafe static extern int ddjvu_page_render(IntPtr page, ddjvu_render_mode_t mode, IntPtr pagerect,
IntPtr renderrect,
IntPtr pixelformat,
ulong rowsize,
[Out][MarshalAs(UnmanagedType.LPArray)]byte[] imagebuffer);Below is how I am calling this function in the c# codebyte* buffer = (byte *)Memory.Alloc(nSize);
try
IntPtr ptr1 = (IntPtr)Memory.Alloc(Marshal.SizeOf(prect));
Marshal.StructureToPtr(prect, ptr1, false);
IntPtr ptr2 = (IntPtr)Memory.Alloc(Marshal.SizeOf(rrect));
Marshal.StructureToPtr(rrect, ptr2, false);
byte[] array = new byte[nSize];
fixed (byte* p = array) Memory.Copy(buffer, p, nSize);
ddjvu_page_render(page, ddjvu_render_mode_t.DDJVU_RENDER_MASKONLY, ptr1, ptr2, fmt, (ulong)stride, array);
finally
Memory.Free(buffer);
}call to ddjvu_page_render in above code is throwing "Attempted to read or write protected memory. This is often an indication that other memory is corrupt."
Prior to this post I must have tried all the option could find in various blogs.
Appreciate any help, is almost a day I am clueless, your timely help could save my job

Answer 1

Thanks Viorel, below is the definition of original C function
DDJVUAPI int
ddjvu_page_render(ddjvu_page_t *page,
const ddjvu_render_mode_t mode,
const ddjvu_rect_t *pagerect,
const ddjvu_rect_t *renderrect,
const ddjvu_format_t *pixelformat,
unsigned long rowsize,
char *imagebuffer );below is how the code is calling this function in C#, the in pointers are all valid pointer I checked in debugging window byte* buffer = (byte *)Memory.Alloc(nSize);
try
IntPtr ptr1 = (IntPtr)Memory.Alloc(Marshal.SizeOf(prect));
Marshal.StructureToPtr(prect, ptr1, false);
IntPtr ptr2 = (IntPtr)Memory.Alloc(Marshal.SizeOf(rrect));
Marshal.StructureToPtr(rrect, ptr2, false);
byte[] array = new byte[nSize];
fixed (byte* p = array) Memory.Copy(buffer, p, nSize);
ddjvu_page_render(page, ddjvu_render_mode_t.DDJVU_RENDER_MASKONLY, ptr1, ptr2, fmt, (ulong)stride, array);
finally
Memory.Free(buffer);