I am developing applications that communicate to a web service to access a database.
One of the web service calls returns data held by a node in a tree structure by taking either the GUID of the node, or NULL to return the root node.
Adding a web service reference to a managed project easily allows null to be sent as a parameter, but from unmanaged code (C++ MSXML and Objective-C/Apple NSWebData) where I build the entire XML request as a string, I cannot send NULL as the guid parameter without getting an invalid GUID error from the host. I have tried as many things as I can think of - "", NULL, "NULL", 0, "0", just blank, an all-zero GUID etc.
I am currently having to specify the GUID of the root node as a workaround, but this will vary in release instances of the database.
Does anyone know how I pass a null GUID?