In general, the VPLUS terminal input/output procedures such
as VOPENTERM, VCLOSETERM, VREADFIELDS and VSHOWFORM are sufficient for most applications that communicate
with a user via a terminal interface.
In building complex user interfaces, however, application
designers have a limited number of tools for implementation. Hence,
they resort to using FREAD, FWRITE, and input/output verbs of their programming language
to display and retrieve information from the terminal when running
VPLUS. The situation becomes more complicated when the application
controls the terminal settings as well as the driver settings, and
is likely to result in an application that runs in a restricted
environment; for example, on an ATP an on one kind of terminal only.
VPLUS provides two additional procedures that help application
designers to write applications with complex user interfaces that
are more portable and easier to maintain. They are VTURNON and VTURNOFF.
