The table in pxt-typ lists the types used in ProXT.
The rule of thumb is that simple types in C are mapped to simple types in Prolog.
In most cases C struct types are represented as handles. A handle is a term whose functor is the type name and whose argument is the address of the structure in memory. The address of a C structure would be of interest to programmers interfacing to foreign code.
Character strings are represented by atoms and arrays are represented by lists.