dde(n) Tcl Bundled Packages dde(n)
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NAME
dde - Execute a Dynamic Data Exchange command
SYNOPSIS
package require dde 1.2
dde servername ?topic?
dde execute ?-async? service topic ?data?
dde poke service topic item data
dde request ?-binary? service topic ?data?
dde services service topic ?data?
dde eval ?-async? service topic ?data?
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DESCRIPTION
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 service name and a topic. Both the service name and topic are applica-tion application
tion defined; Tcl uses the service name TclEval, while the topic name is the name of the interpreter
given by dde servername. Other applications have their own service names and topics. For instance,
Microsoft Excel has the service name Excel.
The eval and execute commands accept the option -async:
DDE COMMANDS
The following commands are a subset of the full Dynamic Data Exchange set of commands.
dde servername ?topic?
dde servername registers the interpreter as a DDE server with the service name TclEval and the
topic name specified by topic. If no topic is given, dde servername returns the name of the
current topic or the empty string if it is not registered as a service.
dde execute ?-async? service topic data
dde execute takes the data and sends it to the server indicated by service with the topic
indicated by topic. Typically, service is the name of an application, and topic is a file to
work on. The data field is given to the remote application. Typically, the application
treats the data field as a script, and the script is run in the application. The -async
option requests asynchronous invocation. The command returns an error message if the script
did not run, unless the -async flag was used, in which case the command returns immediately
with no error.
dde poke service topic item data
dde poke passes the data to the server indicated by service using the topic and item speci-fied. specified.
fied. Typically, service is the name of an application. topic is application specific but
can be a command to the server or the name of a file to work on. The item is also application
specific and is often not used, but it must always be non-null. The data field is given to
the remote application.
dde request ?-binary? service topic item
dde request 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. service is typically the name of an appli-cation, application,
cation, topic is typically the name of the file, and item is application-specific. The command
returns the value of item as defined in the application. Normally this is interpreted to be a
string with terminating null. If -binary is specified, the result is returned as a byte
array.
dde services service topic
dde services returns a list of service-topic pairs that currently exist on the machine. If
service and topic are both null strings ({}), then all service-topic pairs currently available
on the system are returned. If service is null and topic is not, then all services with the
specified topic are returned. If service is not null and topic is, all topics for a given ser-vice service
vice are returned. If both are not null, if that service-topic pair currently exists, it is
returned; otherwise, null is returned.
dde eval ?-async? topic cmd ?arg arg ...?
dde eval evaluates a command and its arguments using the interpreter specified by topic. The
DDE service must be the TclEval service. The -async option requests asynchronous invocation.
The command returns an error message if the script did not run, unless the -async flag was
used, in which case the command returns immediately with no error. This command can be used
to replace send on Windows.
DDE AND TCL
A Tcl interpreter always has a service name of TclEval. Each different interpreter of all running
Tcl applications must be given a unique name specified by dde servername. Each interp is available as
a DDE topic only if the dde servername command was used to set the name of the topic for each interp.
So a dde services TclEval {} command will return a list of service-topic pairs, where each of the
currently running interps will be a topic.
When Tcl processes a dde execute command, the data for the execute is run as a script in the interp
named by the topic of the dde execute command.
When Tcl processes a dde request command, it returns the value of the variable given in the dde com-mand command
mand in the context of the interp named by the dde topic. Tcl reserves the variable $TCLEVAL$EXE-CUTE$RESULT $TCLEVAL$EXECUTE$RESULT
CUTE$RESULT for internal use, and dde request commands for that variable will give unpredictable
results.
An external application which wishes to run a script in Tcl should have that script store its result
in a variable, run the dde execute command, and the run dde request to get the value of the variable.
When using DDE, be careful to ensure that the event queue is flushed using either update or vwait.
This happens by default when using wish unless a blocking command is called (such as exec without
adding the & 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 situa-tion. situation.
tion.
SEE ALSO
tk(n), winfo(n), send(n)
KEYWORDS
application, dde, name, remote execution
dde 1.2 dde(n)
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