Using a C++ library in PostgreSQL

Hi all,
    My research project is based on PostgreSQL. I want to get the Post-Schema-Validation-Infoset (PSVI)

of an XML document being stored. However, the current libxml2 library does not support PSVI at all. So

I have to use the Xerces C++ library in PostgreSQL. But I wonder if it is possible to call a C++ API in

a C code base. 
   Could anyone here give me some guidelines to do it? Can the recently discussed "Mostly Harmless C++"

patch be helpful to what I want to do?