How do I call CA-Clipper code from C?  Can this even be done?

 Date: 25-Nov-91
 X-Contributors: Steve Larsen <76370.1532@compuserve.com>,
  Jobst Hensiek <76656.1606@compuserve.com>

 With versions prior to 5.2, you have to set up Clip's internal
 EVAL stack properly with _xpushf() and _xpopf().  Afterwards,
 call _xdo() to execute the CA-Clipper function.  The whole thing is
 undocumented, and it is discouraged by CA because it requires
 the use of internal functions which are not guaranteed to remain
 unchanged from one CA-Clipper version to the next.  Most people
 spend weeks poking around the symbol tables to get this to work.

 CA-Clipper 5.2e's well-documented Item API (Application Programming
 Interface) allows you to evaluate CA-Clipper expressions, and view
 or change CA-Clipper variables, directly from C code.  You can
 request this documentation free from CA if you have purchased
 CA-Clipper 5.2e.

 It appears to be very difficult if not impossible to call
 CA-Clipper code successfully from within a C "main" program.  The
 environment must be CA-Clipper calling C calling CA-Clipper for
 this stunt to work.