DDE conversations and client syntax

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DDE conversations and client syntax

Two applications participating in Dynamic Data Exchange are said to be engaged in a DDEconversation. The application that initiates the conversation is the DDE Client, and the application that responds to the DDE Client is the DDE server.

An application can have several DDE conversations running at the same time. The application can be the DDE Client in some conversations (requesting data or services), and the DDE server (the data/service provider) in others. Each request or response in a DDE conversation specifies the data or service to be sent or received.

Note: A DDE conversation is sometimes referred to as a channel or a link.

The syntax sent by the DDE Client when it tries to establish a DDE conversation with the DDE server, consists of three parts:

The name of the application to retrieve the data from.
The file or topic name which contains the data to be retrieved.
The cell range, value, field, or data item that's being requested.

These are combined in the format:

<DDE server application name>|<DDE Topic name>!<DDE Data item 
name>

where:

<DDE server applicationname> identifies the DDE server application.
| (pipe character) separates the DDE server application name from the DDE Topic Name with no spaces between them.
<DDE Topic name> identifies the context of the data. For DDE Servers that operate on file-based documents, DDE topic names are typically file names. For other DDE Servers, they are other DDE application-specific strings.
! (exclamation character) separates the DDE Topic Name from the DDE Data item name with no spaces.
<DDE Data item name> is a string that identifies the data item that a DDE server can pass to a DDE Client during a DDE transaction. In some instances, the DDE Data item name is optional. Refer to the DDE application documentation for particulars.

Note: In the DDE Client syntax structure example above, every placeholder shown inside arrow brackets ( <placeholder> ) has to be replaced with the actual name of the item that it describes. Do not include the arrow brackets and the placeholder words they contain in the statement, and are shown here only for your information.

As the DDE protocol was designed in an era before long file names, DDE only supports the use of short (8 character) file names. To overcome this limitation, enclose the three parts of the DDE syntax within single quotes respectively. For example:

Citect|Variable!'Process Variable 1'

This instructs DDE to treat the characters within the quotes as strings, thus permitting them to contain long file names, the space character ( ), the pipe character (|), the exclamation or bang character (!), or any other non alphanumeric character.