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dde(n) Tcl Bundled Packages dde(n) 





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 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 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 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 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 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 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-lang.org/








SEE ALSO


tk(n), winfo(n), send(n)






KEYWORDS


application, dde, name, remote execution







  

    1.4
    dde