Node:Handling Exceptions in Visual Basic, Previous:Evaluating a Query with Side-Effects, Up:How to Call Prolog from Visual Basic
If an exception has been raised during Prolog execution, the functions
PrologQueryCutFail or PrologNextSolution return -1. To
access the exception term, the procedure PrologGetException
can be used. This procedure will deposit the exception term in
string format into an output parameter, as if written via the
writeq/2 predicate.
Example:
when the following code fragment is executed, the message box will
display the domain_error(_1268 is 1+a,2,expression,a) error
string.
Dim exc As String
qid = PrologOpenQuery("X is 1+a")
If PrologNextSolution(qid) < 0 Then
PrologGetException(exc)
Msg exc,48,"Error"
End if