.. highlightlang:: us

.. index:: DdeCallback_Request

.. _ddecallback_request:

DdeCallback_Request
===================

.. us.tag  DdeCallback_Request ENGLISH

:ref:`DdeCallback_Request` is called by the client to request data from UniPlot.

.. function::  ssData = DdeCallback_Request(hConv, ssItem, ssTopic)

.. us.return

**Return Value**

*ssData* is a scalar string.

.. us.params

**Parameters**

.. uparam:: hConv

   *hConv* is the channel number.

.. uparam:: ssItem

   *ssItem* is the item name.

.. uparam:: ssTopic

   *ssTopic* is the topic name.

.. us.example

**Example**

The following Word-Basic program requests the date from UniPlot:

.. highlight:: basic

::

   Sub Main
       chan = DDEInitiate("UniPlotSL", "test")
       StrResult$ = DDERequest$(chan, "date")
       MsgBox(StrResult$)
       DDETerminate(chan)
   End Sub

.. highlight:: us

The Basic command ``StrResult$ = DDERequest$(chan, "date")``, requests the
current date from UniPlot. To do so, we have to make the following changes to the
:ref:`DdeCallback_Request` function in :file:`UniPlot/script/obj_dde.ic` file:

::

   def DdeCallback_Request(hConv, ssItem, ssTopic)
   {
       // this line is for debug purpose only
       printf("---Request---\n");
       printf("Conversation-No.: %x, Item: %s, Topic: %s\n\n", ..
           hConv, ssItem, ssTopic);
       if (ssTopic == "date") {
       return "Today is the " + sum(date());
       }
       return "OK";
   }

The standard DDE callback function of UniScript will create the
following output into the command window:

::

   ---Connect---
   Service: UniPlotSL, Topic: xyz

   ---ConnectConfirm---
   Conversation-No.: 21000d00, Service: UniPlotSL, Topic: xyz

   ---Request---
   Conversation-No.: 21000d00, Item: xyz, Topic: date

   ---Disconnect---
   Conversation-No.: 21000d00

.. seealso::
   :ref:`overview-dde`,
   :ref:`DdeCallback_Connect`,
   :ref:`DdeCallback_ConnectConfirm`,
   :ref:`DdeCallback_Disconnect`,
   :ref:`DdeCallback_Poke`,
   :ref:`DdeCallback_Execute`

:sub:`id-724605`