The marshaler wraps the call to the unmanaged function in a hidden wrapper routine that pins and copies the managed string into a locally allocated string in the unmanaged context, which then is passed to the unmanaged function. When the unmanaged function returns, the wrapper either deletes the resource, or if it was on the stack, it is reclaimed when the wrapper goes out of scope. The unmanaged function is not responsible for this memory. The unmanaged code only creates and deletes memory in the heap set up by its own CRT, so there is never an issue with the marshaller using a different CRT version.