dde
Section: Tcl Bundled Packages (n)
Updated: 1.4
Page Index
NAME
dde - Execute a Dynamic Data Exchange command
SYNOPSIS
package require dde 1.4
dde servername ?-force? ?-handler proc? ?--? ?topic?
dde execute ?-async? ?-binary? service topic data
dde poke ?-binary? service topic item data
dde request ?-binary? service topic item
dde services service topic
dde eval ?-async? topic cmd ?arg arg ...?
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 application 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.
DDE COMMANDS
The following commands are a subset of the full Dynamic Data Exchange
set of commands.
- dde servername ?-force? ?-handler proc? ?--? ?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. If the given topic name is already in use, then a
suffix of the form
`` #2''
or
`` #3''
is appended to the name to make it
unique. The command's result will be the name actually used. The
-force option is used to force registration of precisely the
given topic name.
-
The -handler option specifies a Tcl procedure that will be called to
process calls to the dde server. If the package has been loaded into a
safe interpreter then a -handler procedure must be defined. The
procedure is called with all the arguments provided by the remote
call.
- dde execute ?-async? ?-binary? 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.
Without the -binary option all data will be sent in unicode. For
dde clients which don't implement the CF_UNICODE clipboard format, this
will automatically be translated to the system encoding. You can use
the -binary option in combination with the result of
encoding convertto to send data in any other encoding.
- dde poke ?-binary? service topic item data
-
dde poke passes the data to the server indicated by
service using the topic and item specified. 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.
Without the -binary option all data will be sent in unicode. For
dde clients which don't implement the CF_UNICODE clipboard format, this
will automatically be translated to the system encoding. You can use
the -binary option in combination with the result of
encoding convertto to send data in any other encoding.
- 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 application,
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 empty strings ({}), then all service-topic pairs currently
available on the system are returned. If service is empty and
topic is not, then all services with the specified topic are
returned. If service is non-empty and topic is, all topics
for a given service are returned. If both are non-empty, if that
service-topic pair currently exists, it is returned; otherwise, an
empty string 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 command in the context of the interp named by the
dde topic. Tcl reserves the variable $TCLEVAL$EXECUTE$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 then 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
situation.
EXAMPLE
This asks Internet Explorer (which must already be running) to go to a
particularly important website:
-
package require dde
dde execute -async iexplore WWW_OpenURL http://www.tcl.tk/
SEE ALSO
tk(n),
winfo(n),
send(n)
KEYWORDS
application, dde, name, remote execution