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'\" The definitions below are for supplemental macros used in Tcl/Tk
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.TH dde n 8.1 Tcl "Tcl Built-In Commands"
.BS
'\" Note:  do not modify the .SH NAME line immediately below!
.SH NAME
dde \- Execute a Dynamic Data Exchange command
.SH SYNOPSIS
.sp
\fBpackage require dde 1.1\fR
.sp
\fBdde \fIservername \fR?\fItopic\fR?
.sp
\fBdde ?\-async?\fR \fIcommand service topic \fR?\fIdata\fR?
.BE

.SH DESCRIPTION
.PP
This command allows an application to send Dynamic Data Exchange (DDE)
command when running under Microsoft Windows. Dynamic Data Exchange is
a mechanism where applications can exchange raw data. Each DDE
transaction needs a \fIservice name\fR and a \fItopic\fR. Both the
\fIservice name\fR and \fItopic\fR are application defined; Tcl uses
the service name \fBTclEval\fR, while the topic name is the name of the
interpreter given by \fBdde servername\fR. Other applications have their
own \fIservice names\fR and \fItopics\fR. For instance, Microsoft Excel
has the service name \fBExcel\fR.
.PP
The only option to the \fBdde\fR command is:
.TP
\fB\-async\fR
Requests asynchronous invocation.  This is valid only for the
\fBexecute\fR subcommand. Normally, the \fBdde execute\fR subcommand
waits until the command completes, returning appropriate error
messages. When the \fB\-async\fR option is used, the command returns
immediately, and no error information is available.
.SH "DDE COMMANDS"
.PP
The following commands are a subset of the full Dynamic Data Exchange
set of commands.
.TP
\fBdde servername \fR?\fItopic\fR?
\fBdde servername\fR registers the interpreter as a DDE server with
the service name \fBTclEval\fR and the topic name specified by \fItopic\fR.
If no \fItopic\fR is given, \fBdde servername\fR returns the name
of the current topic or the empty string if it is not registered as a service.
.TP
\fBdde execute \fIservice topic data\fR
\fBdde execute\fR takes the \fIdata\fR and sends it to the server
indicated by \fIservice\fR with the topic indicated by
\fItopic\fR. Typically, \fIservice\fR is the name of an application,
and \fItopic\fR is a file to work on.  The \fIdata\fR field is given
to the remote application. Typically, the application treats the
\fIdata\fR field as a script, and the script is run in the
application. The command returns an error if the script did not
run. If the \fB\-async\fR flag was used, the command
returns immediately with no error.
.TP
\fBdde poke \fIservice topic item data\fR
\fBdde poke\fR passes the \fIdata\fR to the server indicated by
\fIservice\fR using the \fItopic\fR and \fIitem\fR specified.  Typically,
\fIservice\fR is the name of an application.  \fItopic\fR is application
specific but can be a command to the server or the name of a file to work
on.  The \fIitem\fR is also application specific and is often not used, but
it must always be non-null.  The \fIdata\fR field is given to the remote
application.
.TP
\fBdde request \fIservice topic item\fR
\fBdde request\fR is typically used to get the value of something; the
value of a cell in Microsoft Excel or the text of a selection in
Microsoft Word. \fIservice\fR is typically the name of an application,
\fItopic\fR is typically the name of the file, and \fIitem\fR is
application-specific. The command returns the value of \fIitem\fR as
defined in the application.
.TP
\fBdde services \fIservice topic\fR
\fBdde services\fR returns a list of service-topic pairs that
currently exist on the machine. If \fIservice\fR and \fItopic\fR are
both null strings ({}), then all service-topic pairs currently
available on the system are returned. If \fIservice\fR is null and
\fItopic\fR is not, then all services with the specified topic are
returned. If \fIservice\fR is not null and \fItopic\fR is, all topics
for a given service are returned. If both are not null, if that
service-topic pair currently exists, it is returned; otherwise, null
is returned.
.TP
\fBdde eval \fItopic cmd \fR?\fIarg arg ...\fR?
\fBdde eval\fR evaluates a command and its arguments using the
interpreter specified by \fItopic\fR. The DDE service must be the
\fBTclEval\fR service.  This command can be used to replace send on
Windows.
.SH "DDE AND TCL"
A Tcl interpreter always has a service name of \fBTclEval\fR.  Each
different interpreter of all running Tcl applications must be
given a unique
name specified by \fBdde servername\fR. Each interp is available as a
DDE topic only if the \fBdde servername\fR command was used to set the
name of the topic for each interp. So a \fBdde services TclEval {}\fR
command will return a list of service-topic pairs, where each of the
currently running interps will be a topic.
.PP
When Tcl processes a \fBdde execute\fR command, the data for the
execute is run as a script in the interp named by the topic of the
\fBdde execute\fR command.
.PP
When Tcl processes a \fBdde request\fR command, it returns the value of the
variable given in the dde command in the context of the interp named by the
dde topic. Tcl reserves the variable \fB$TCLEVAL$EXECUTE$RESULT\fR for
internal use, and \fBdde request\fR commands for that variable will give
unpredictable results.
.PP
An external application which wishes to run a script in Tcl should have
that script store its result in a variable, run the \fBdde execute\fR
command, and the run \fBdde request\fR to get the value of the
variable.
.PP
When using DDE, be careful to ensure that the event queue is flushed
using either \fBupdate\fR or \fBvwait\fR.  This happens by default
when using \fBwish\fR unless a blocking command is called (such as \fBexec\fR
without adding the \fB&\fR to place the process in the background).
If for any reason the event queue is not flushed, DDE commands may
hang until the event queue is flushed.  This can create a deadlock
situation.

.SH "SEE ALSO"
tk(n), winfo(n), send(n)

.SH KEYWORDS
application, dde, name, remote execution