Returns an integer containing the last error number. If no error was reported 0 is returned.
link resource is passed to
ingres_errno() it returns the last error recorded for
the link. If no link is passed then ingres_errno()
returns the last error reported using the default link.
The function, ingres_errno(), should always be called after executing a database query. Calling another function before ingres_errno() is called, will reset or change any error code from the last Ingres function call.