Purpose
Returns a data value obtained from a DDE conversation.
Syntax
DDERequest$( channel, itemname )channel is an integer channel number returned by the DDEInitiate() function.
itemname is a string representing the name of an item in the server application.
Return Value
String
Description
The DDERequest$() function returns a string of information obtained through a DDE conversation. If the request is unsuccessful, the DDERequest$() function returns a null string.
The channel parameter must correspond to the number of a channel which was opened through the DDEInitiate() function.
The itemname parameter should identify an item which is appropriate for the specified channel. Different DDE applications support different item names; to learn what item names are supported by a particular Windows application, refer to the documentation for that application.
The following table lists some topic and item combinations that can be used when conducting a DDE conversation with Microsoft Excel as the server:
| Topic name | Item names to use with DDERequest$() |
|---|---|
| "System" | "Systems" returns a list of item names accepted under the "System" topic;
"Topics" returns a list of DDE topic names accepted by Excel, including the names of all open worksheets; "Formats" returns a list of clipboard formats accepted by Excel (for example, "TEXT BITMAP ...") |
| wks (name of a worksheet in use) | A string of the form R1C1 (for Row 1, Column 1) returns the contents of that cell |
| Topic name | item names to use with DDERequest$() |
|---|---|
| "System" | "Systems" returns a list of item names accepted under the "System" topic;
"Topics" returns a list of DDE topic names accepted by MapInfo Pro, which includes the names of all MapBasic applications currently in use; "Formats" returns a list of clipboard formats accepted by MapInfo Pro ("TEXT"); "Version" returns the MapInfo version number, multiplied by 100. |
| mbx (name of .MBX in use) | "{items}" returns a list of the names of global variables in use by the specified MapBasic application; specifying the name of a global variable lets DDERequest$() return the value of the variable |
Error Conditions
ERR_CMD_NOT_SUPPORTED (642) error generated if not running on Windows.
ERR_INVALID_CHANNEL (696) error if the specified channel number is invalid.
ERR_CANT_INITIATE_LINK (698) error generated if MapBasic cannot link to the topic.
Example
The following example uses the DDERequest$() function to obtain the current contents of the first cell in an Excel worksheet. Note that this example will only work if Excel is already running.
Dim i_chan_num As Integer
Dim s_cell As String
i_chan_num = DDEInitiate("EXCEL", "Sheet1")
s_cell = DDERequest$(i_chan_num, "R1C1") The following example assumes that there is another MapBasic application currently in use―"Dispatch"―and assumes that the Dispatch application has a global variable called Address. The example below uses DDERequest$() to obtain the current value of the Address global variable.
Dim i_chan_num As Integer, s_addr_copy As String
i_chan_num = DDEInitiate("MapInfo","C:\DISPATCH.MBX")
s_addr_copy = DDERequest$(i_chan_num, "Address") See Also:
DDEInitiate() function