Convert from C++/CLI pointer to native C++ pointer

Question

I have run in to this problem of converting a C++/CLI pointer to a native C++ pointer. Heres the background: I\'m writing a windows forms application using C++/CLI. The appl

Answer 1

I believe you have to mark the pointer as 'pinned' (in the managed code) and then copy the bytes over to some unmanaged memory region, and then use the pointer to that. For instance, here's a piece of code I once got somewhere which converts a pointer to a managed System::String to an UTF-8 encoded unmanaged std::string:

std::string managedStringToStlString( System::String ^s )
{
    Encoding ^u8 = Encoding::UTF8;
    array ^bytes = u8->GetBytes( s );
    pin_ptr pinnedPtr = &bytes[0];
    return string( (char*)pinnedPtr );
}

Note how I've got to get a 'pinned' pointer to the bytes array returned by the GetBytes() function, and then cast that to char* before passing it to the std::string constructor. I believe this is necessary to avoid that the managed memory subsystem moves the bytes array around in memory while I'm copying the bytes into the STL string.

In your case, try replacing

CoCreateInstance(rclsid, pUnkOuter, dwClsContext, riid, (void**)(&provider)); 

with

pin_ptr pinnedPtr = &provider;
CoCreateInstance(rclsid, pUnkOuter, dwClsContext, riid, (void**)pinnedPtr); 

and see whether that works.