Calling Clipper functions from C

 One of the more common calls we receive in Technical Support is the
 question about calling a Clipper UDF from C.   It is commonly thought
 that if C can be called from Clipper, then Clipper  functions and C
 functions must be operate identically.  This is not the case.
 Anyone familiar with the way C calls a function knows that C pushes
 strongly-typed arguments on the processor stack and then does a jump
 to the function that is being called.  Clipper does not use the
 processor stack for the passing of arguments to functions.  Clipper
 functions operate within an "activation context" that must be
 established before the Clipper function is called.  This allows
 Clipper to support loosely-typed arguments, variable number of
 arguments, as well as functions such as PROCNAME().   This means that
 even if you succeeded in calling a Clipper function, you would be
 unable to pass it parameters, and it would be operating "out of
 context."

 The extend system also assumes that it has complete control over
 virtual memory while you are executing a C or assembler function.  If
 you call a Clipper function, this assumption is no longer valid and
 may cause the system to crash.  Certain Clipper operations are also
 inherently problematic:  what happens if the Clipper function BREAKs
 (or calls the error handler and it BREAKs)?  There is no equivalent C
 ability.