Global variable in an event loop

Hi,
I have a global variable from one VI and want to read it in another VI but
only if the value has changed, i want to do it with an event case but it
doesn't do any thing when a read my Global variable in an event when the
value has changed?
Does anyone knows how to do this?
Best regards,
Thijs

You'll either need to generate a user event, or set the value using a value (signaling) property and let the "listener" create a dynamic value change event based on a reference to the indicator in use.
With user event:
Create a user event and give both the VI that is to react to a change event and the global (functional global) a reference to that event. Inside the global you check if the value differs from the previous one whenever it is written to, and if it is then fire the event.
MTO

Similar Messages

  • Can not use Global Variable in Event Structure

    I am using LabVIEW 2009.
    In my LabView project I have a Boolean Global variable called EStop. I can read and write the Global variable. If I double click on the Global variable, it takes me to EStop.vi which includes a Text Button. EStop.vi is part of my Project.
    In one of my VIs, I have an Event Structure. If I go to one of the Event Handlers in that Event Structure and right click and then select Add Event Case, I get a list of possible events. But that list does not include EStop or an EStop events.
    I want to Add an Event Case for EStop: Value Changed.
    Why can't I Add events to an Event Case that include events on Global Variables like value changed?
    How do I add EStop: value changed event to my Event Structure.
    Solved!
    Go to Solution.

    dbaechtel wrote:
    I have many events throughout the system that might need to cause the system to do an Emergency Stop action. So I want ro use a Global variable that is accessible from anywhere in the system. Any action or condition that occurs anywhere in the system can activate the emergency Stop condition by setting the boolean EStop Global variable to True. When the Global bolean variable goes true(value changed), I want to detect that event in an Event Structure and do the actions necessary to accomplish a system Emergency Stop.
    Sorry, I am not familiar with your terminologies. What is your definition of a "system".
    One big VI with many parallel loops?
    Several VIs running in parallel?
    LabVIEW Champion . Do more with less code and in less time .

  • Problem using local variable in event loop

    I have a state machine from which I want to monitor various controls, including "Start" and "Stop" buttons.  Not every state needs to monitor the controls.  At present, most states run timed loops.  In the first state that reads the front panel, I have an Event structure (inside a While loop) that monitors the various controls' Change Value events.  For numeric controls, I update variables (in shift registers) as needed.  The "Start" button is used to end the While loop controlling the Event structure, allowing the State to exit to the next state.
    My problem comes in subsequent states that employ this same idea.  Here, I put a Local Variable bound to the Start button and use the same code, but it frequently happens that when I enter this particular state, I cannot "turn on" the control -- I push the button, but it stays off.  Curiously, if it was On when I enter, I can turn it off, but then I'm stuck not being able to turn it on.
    I mocked up a very simply routine that illustrates this.  There are two sequences (corresponding to the two states).  Both use an Event loop with a local variable bound to my Stop button (really this is an LED control with custom colors).  I've deliberately moved the "initialization" (the declaration of the control in the block diagram) out of the Event loops -- putting it inside the first loop modifies the behavior in another strange way.
    Here's my thinking on how I would expect this to work:  The code outside Event Loop 1 should have little effect.  Assume the Stop button is initially Off.  You will "sit" in Event Loop 1 until you push the Stop button, changing its value to True; this value will be passed out of the Event case and cause the first While loop to exit.  You now enter the second sequence.  As I understand the Exit tunnel, it defaults to "False", so I'd expect to stay in the second Event loop until I turn the Stop button from On to Off, which will pass out a False, and keep me in the While for one more button push.  However, this doesn't happen -- I immediately exit, as though the "True" value of the Stop local variable is being seen and recognized by the Event loop (even though it hasn't changed, at least not in the context of this second loop).
    An even more curious thing occurs if I start this routine with the Stop button turned on.  Now I start in my Event loop waiting for a change, but this time the change will be from On to Off, which won't cause an exit from the frame.  This will be reflected by having the While loop count increment.  We should now be in the state of the example above, i.e. in an Event loop waiting for the control to be pushed again, and turned On.  However, clicking the control has no effect -- I cannot get it to "turn on".
    Where am I going astray in my thinking?  What is it about this method of doing things that violates the Labview paradigm?  As far as I can tell, what I'm doing is "legal", and I don't see the flaw in my reasoning, above (of course not -- otherwise I'd have fixed it myself!).  Note that because I'm using local variables inside Event loops (and I'm doing this because there are two places in my code where I want to do such testing), the Stop control is not latching (as required).  Is there something that gets triggered/set when one reads a latched control?  Do I need to do this "manually" using my local variable?
    I'll try to attach the simple VI that illustrates this behavior.
    Bob Schor
    Attachments:
    Simple Stop Conundrum.vi ‏14 KB

    altenbach wrote:
    Ravens Fan wrote:
    NEVER have multiple event structures that share the same events. 
    Actually, that's OK.  NOT OK is having multiple event structures in the same sequence structure.
    See also: http://forums.ni.com/ni/board/message?board.id=170&message.id=278981#M278981
    That's interesting.  I had always thought I read more messages discouraging such a thing rather than saying it was okay.  Your link lead me to another thread with this message. http://forums.ni.com/ni/board/message?board.id=170&message.id=245793#M245793.  Now that thread was mainly concentrating on registered user events which would be a different, but related animal. 
    So if you have 2 event structures they each have their own event queue?  So if you have a common event, one structure pulls it off its event queue and it does not affect the other structure's event queue?  I guess the inherent problem with this particular VI was that the second event structure locked the front panel.  Since the code never got to that 2nd event structure because the  first loop never stopped because the change was from true to false.  After reading your post and the others, I did some experimentation and turned off the Lock front panel on the 2nd structure, and that prevented the lockup of the program.
    Overall, the example VI still shows problems with the architecture and I think your answer should put the original poster on the right track.  I think as a rule I would probably never put the same event in multiple structures, I feel there are better ways to communicate the same event between different parts of a program,  but I learned something by reading your reply and about how the event structures work in the background.  Thanks.

  • Function REUSE_ALV_GRID_DISPLAY, events and global variables

    Hi everybody,
    in a report I use FM REUSE_ALV_GRID_DISPLAY with a registered callback for event 'USER_COMMAND'.
    In the callback-form I want to change the internal table, which I provided for displaying to REUSE_ALV_GRID_DISPLAY.
    How can I access the internal table in the callback-form without using global variables?.
    Kind regards,
    Hubert
    Edited by: Hubert Heitzer on Feb 23, 2011 4:13 PM
    This is not the solution I asked for, but I found a workaround.
    I created a function group, which encapsulates the internal table.
    A function provides the service for colleting data for the internal table and displays the ALV.
    The callback-form is also a member of my function group and is therefore able to access the internal table.

    Hi everybody,
    in a report I use FM REUSE_ALV_GRID_DISPLAY with a registered callback for event 'USER_COMMAND'.
    In the callback-form I want to change the internal table, which I provided for displaying to REUSE_ALV_GRID_DISPLAY.
    How can I access the internal table in the callback-form without using global variables?.
    Kind regards,
    Hubert
    Edited by: Hubert Heitzer on Feb 23, 2011 4:13 PM
    This is not the solution I asked for, but I found a workaround.
    I created a function group, which encapsulates the internal table.
    A function provides the service for colleting data for the internal table and displays the ALV.
    The callback-form is also a member of my function group and is therefore able to access the internal table.

  • How to creat a global variable?

    I want to creat a start button of global variable to control different programs in the sequence structure. But I do not know how to creat it. Thanks for answering.
    Solved!
    Go to Solution.

    Perry Liu wrote:
    Thanks for answering. I attached the code below.
    What I want to do is to combine Get Voc/Isc and GO buttons (shown in the front panal) to one button, and also combine Setup Linear Stair Sweep and start sweep together. I do now find a good way to do that. Thanks so much for your kind help.
    There is no "Get Voc/Isc" or "GO" button anywhere on the front panel, and I have no idea what you mean by "Setup Linear Stair Sweep" and "start sweep". Are you sure you uploaded the correct code?
    Other VI comments:
    You are abusing/misusing global variables. 
    You already have a state machine, so you can actually code this using just the state machine without actually needing the separate event structure loop. Even if you do keep it, that still does not require you to use global variables.
    Why do you have a loop around the Write to Spreadsheet File? This serves no purpose and actually stops your code in that loop until the Stop global is set. This doesn't make much sense.
    Since you do not have a path wired to the Write to Spreadheet File VI, you will be asked for a path each time the loop iterates. Use a shift register to hold the value of the path from iteration to iteration.
    Get rid of the Build XY Graph Express VI and those Convert to Dynamic Data functions. Replace with a single Bundle function.

  • Use global variable to transfer user parameter in some Vi

    Hello,
    I have troubles when I use a global variable to transfer the parameter to a first Vi (user interface) to a second vi (acquisition interface).
    In the first Vi, the user paramater is wrote to my global variable.
    In the second Vi, the acquisition parameter is read to my global variable.
    This 2 Vis are include to a master Vi who synchronized by the error bus.
    The problem :
    For the first use, the user parameter is transfer to the global variable but the acquisition vi read the old parameter. In the second use, acquisition vi read the first use parameter.
    After I use the IN/OUT parameter subvi and i have too this problem.
    Thanks for help.
    VIEW THE PROBLEM : (I use event structure
    Attachments:
    Problem.zip ‏52 KB

    Labview uses the dataflow to chain the execution. That is, as soon as one item of data is ready is is presented to the next stage.
    Global (or local) variables do not easily fit in there. A variable is always present and ready to give away it's data. It does not matter that you write to it in one vi. Another vi, that is running concurrently is not aware that the content may have changed.
    Especially if you reference variables outside of loops, the value is taken just once and never updated. Be aware! If in doubt, use the tracing facilty (the light bulb) to follow the data flow.
    Gabi
    7.1 -- 2013
    CLA

  • Loading a text file into a global variable issue - really a global var?

    From all the documentation and examples I can find, it appears that it would be
    correct to create a global array variable [outside of any functions] to load image names into,
    then use these images for a slideshow. I want to make the app dynamic, in that changing the text file gives a new set of images.
    The global variable goes null [no values] after the load event listener. Why is that?
    Isn't global, well global, and alive for the duration of the SWF?
    PARAMS.TXT:
    monthNames=January,February,March,April,May,June,July,August,September,October,November,De cember&dayNames=Sunday,Monday,Tuesday,Wednesday,Thursday,Friday,Saturday
    CODE:
    var dNames:Array = new Array();
    var mNames:Array = new Array();
    var request:URLRequest = new URLRequest("images/params.txt");
    var variables:URLLoader = new URLLoader();
    variables.dataFormat = URLLoaderDataFormat.VARIABLES;
    variables.addEventListener(Event.COMPLETE, completeHandler);
    try
    variables.load(request);
    catch (error:Error)
    trace("Unable to load URL: " + error);
    trace("2 mNames 2: " + mNames[2]);
    trace("2 dNames 3: " + dNames[3]);
    stop();
    function completeHandler(event:Event):void
    var loader:URLLoader = URLLoader(event.target);
    dNames = loader.data.dayNames.split(",");
    mNames = loader.data.monthNames.split(",");
    trace(loader.data.dayNames);
    trace("1 mNames 2: " + mNames[2]);
    trace("1 dNames 3: " + dNames[3]);
    OUTPUT:
    2 mNames 2: undefined
    2 dNames 3: undefined
    Sunday,Monday,Tuesday,Wednesday,Thursday,Friday,Saturday
    1 mNames 2: March
    1 dNames 3: Wednesday
    How do I access these values after loading from the external file, after the load?
    Thanks in advance.

    The statement you quoted from whatever Adobe documentation is correct.
    If you want to load the data into the arrays before anything else happens, then have anything else that happens execute via the completeHandler function... after the data is loaded and processed into the arrays.
    the command: loadFile() executes before the trace("2:" +images[4]); command.  The loadFile function is processed and the loading process BEGINS... but starting the loading does not delay the main processing from continuing down the line--the loading itself becomes a secondary/background task.  The command was to execute the loadFile function and the processing of that function was completed.  If you don't believe so, then add a trace...
    function loadFile():void
         vars.dataFormat = URLLoaderDataFormat.VARIABLES;
         vars.addEventListener(Event.COMPLETE, onComplete, false, 0, true);
         vars.load(new URLRequest("images/fnames.txt"));
         trace("started loading");
    If you add that trace, you should see that the loadFile function execution is completed and the next line in your code is then processed... trace(2....)
    The addEventlistener does not stop anything.  The addEventListener code is assigning a monitor, not a traffic controller... it is telling the monitor to indicate when the data has finished loading.  It is not telling anything to stop program execution.
    So if you want to wait until the data is loaded before you do anything else... it goes....
    function onComplete(evt:Event):void
         var urlVars:URLVariables = evt.target.data;
         images = vars.data.images.split(",");
         tnails = vars.data.thumbnails.split(",");
         ................HERE.................

  • How do I add a global variable to my app?

    Hi all,
    I am building a flex app which displays data in different tabs from a mysql database and I wan't to add a sign in process to make sure only registered users of the mysql db can see the data.
    To achieve this I built a sign in component which accepts a username, password and the name of the database to connect to. My flex app then uses a php script to verify that the user can connect to the database using the details entered. If not, the sign in component displays an error message, but if sign in details are verified then the user can see the data from the database.
    How can I store the details in the flex app for that users session so that when the user queries the db for data, flex uses the details entered during the sign in process to connect to the mysql db and submit the query?
    I thought about storing the details as an array in a global variable and then accessing that global variable from anywhere in my app but I don't know if that is the correct/secure way to do what I want, nor do I know how to do it. Any help would be much appreciated.
    Thanks in advance,
    xander

    quick, dirty example, could be improved on but it'll get you rolling;
    After user login has succeeded, send off another HTTP service eg;
    ========
    <mx:Script>
             <![CDATA[
                public var whateverUserNameWasEntered:String;
                 public var whateverUserPasswordEntered:String;
         public function onLoginSuccess():void
              whateverUserNameWasEntered:String = loginbox.text;
              whateverUserPasswordEntered:String = passwordbox.text;
              storeSessionStuff.send();
         ]]>
        </mx:Script>
    <mx:HTTPService id="storeSessionStuff" showBusyCursor="true" method="POST"  url="http://localhost/store.php" useProxy="false">
            <mx:request xmlns="">   
              <username>
                   {whateverUserNameWasEntered}
              </username>
              <password>
                   {whateverUserPasswordEntered}
              </password>       
            </mx:request>
        </mx:HTTPService>          
    ========
    direct it to the php file.....
    <?php
    session_start();
    $_SESSION['username'] = $_POST['username'];
    $_SESSION['password']   = $_POST['password'];
    ?>
    Then, whenever you want to get the information out of the Session, send off another HTTP Service...;
    <mx:HTTPService id="getSessionStuff" result="storeData(event)" showBusyCursor="true" method="POST"  url="http://localhost/get.php" useProxy="false"/>
    to the php file....
    <?php
    session_start();
    print "<details><username>".$_SESSION['username']."</username><password>".$_SESSION['password'] ."</password></details>";
    ?>
    which, you need a result function for:
    <mx:Script>
             <![CDATA[
              private function storeData(evt:ResultEvent):void
                    var username:String;
                    var password: String;
                   username = evt.result.details.username;    
                   password = evt.result.details.password;         
          ]]>
    </mx:Script>
    ta daa
    (if thats what you meant)

  • Function module Global variables not cleared from memory?

    Hi,
    This is may be simple & stupid question ( after posting  4242 posts ):)
    " Declaration in TOP
    data : begin of i_y1yatt occurs 0.
            include structure y1yatt.
    data : end of i_y1yatt.
    types: begin of t_yatt71.
           include structure yatt71.
    types: tcode like sy-tcode.
    types: dflag type c.
    types: end of t_yatt71.
    data : i_yatt71 type standard table of t_yatt71
                   with default key  with header line  initial size 0.
    This is code in the function module.
      loop at i_y1yatt.
        move-corresponding o_y1yatt to i_yatt71.
        if i_y1yatt-werks eq 'N501'.
           move space to i_yatt71-werks.
        endif.
        append i_yatt71. 
        " Here this internal contains the previous entry
        clear i_yatt71.
      endloop.
    This function module is called 25 times in a minute.
    My problem is this
    For example : 1st tranmission is called this fm with 50 records,
    and 2nd tranmission is called fm with 10 records.
    My results are showing
    last record in the 1st transmission is still on the memory while calling 2nd transmission.  ( Here in int table I_YATT71 still contains the 1st transmission's last records during the 2nd tranmission call)
    As per my knowledge if each time calls comes in to fm all gloabl variables get cleared. but some how this not happening.
    Anybody come across this scenario.
    PS. I know i need to use clear statement within the loop as first statement.
    a®

    You must understand that when calling a FM, you load the entire function group into memory. IF there are global variables, then they are "alive" for the entire duration of the program execution. Meaning if you call the function numerious times, or even if you call another function within the same function group, the functions still have access to that same global variable space, so it must always be cleared manually by the developer at the required points.  You can not rely on the runtime to clear the global variables at the end of the function call.  So you should clear all you globals as the first operation in your function module call, if that is what is required.
    Is this clear?
    Regards,
    Rich Heilman

  • Problems in syncronyzing two threads into Test Stand using a Global Variable (TestStand 4.1.1)

    I have one thread that is doing TCPIP Aquisition into a Global variable defined in Teststand. And I have another thread that it supose to read it. All are in the same sequence and execution. The problem is that the aquisition thread got a lot of bytes, while the processing thread is reading always only a few. Do you know what the problem could be?
    I will attach also some pictures just to be maybe more clear...
    Attachments:
    Implementation_pictures.zip ‏368 KB

    I wasn't looking at your Sequence, I was looking at Receive_HDL_Block.JPG. What is that VI doing (the one with number 3 on the icon and Size_in_bytes as an input) ?
    Where in teststand are you doing any checking?
    I don't really understand your sequence.
    You have a sequence (running in a new thread) (why), following by another called Receiver Handler (also running in a new thread) then two more sequences which seem to do some with transmitting something (also running as new threads). You are only waiting on one of these threads (the Receiver Handler). There does seem to be any loops in TestStand, you dont seem to be bothered about the other threads that you have running. What happens when this test sequence finally does stop, what is stopping the Threads that you have running.
    Your pictures dont really seem to fit in with your Test Sequence, such as where does Test_005.vi fit into everything
    The whole thing is a bit of a nightmare.
    Maybe your best bet would be to scrap the lot and start again. Only this time have a better understanding of what you what to achieve, what would be best to put into Teststand and what to put into labview. Whether you really need all those new threads running.
    Sorry to be so blunt.
    Regards
    Ray Farmer
    Regards
    Ray Farmer

  • Global Variables in Flash CS4 (AS3) ?

    Hi,
    I  have another problem with my new project and I am looking to get answers for these two question:
    1.) Is there a way to define a global variable which can be accessed inside and movie clip or button? (where do you define it? is it changeable? can you pass it in by reference?)
    2.) If i have my main stage with some actionscript and a movie clip which has also some action script, IN WHICH ORDER does it execute?
    Thank you in advance for any help and tips!

    Thank you this is what i needed I got it to work now!
    But I do still have one last question on this topic.
    This is the Code:
    //this is in a file Actionscript File called glo.as
    package{
         public class glo{
              public static var widthOfSlider:Number = 5;
    // This code is in scene 1 > my_mc
    import glo;
    trace(glo.widthOfSlider);
    //This code is in scene 1 > my_mc > myNext_mc
    import glo;
    var numOfCovers = 6;
    var temp = glo.widthOfSlider;
    trace(glo.widthOfSlider);
    this.addEventListener(Event.ENTER_FRAME, centerB);
    function centerB(event:Event):void{
         for(var i = 0; i < numOfCovers ; i++ ){
              this["cover_btn_"+String(i)].y = 0;
              this["cover_btn_"+String(i)].x = temp;
              temp += this["cover_btn_"+String(i)].width + 5;
         glo.widthOfSlider = temp;
         trace(glo.widthOfSlider);
         this.removeEventListener(Event.ENTER_FRAME, centerB);
    When I run this I get the following output:
    5
    5
    5
    725.45
    725.45
    The first "5" is from the trace(glo.widthOfSlider); in scene 1 > my_mc
    The next two "5"'s are from the trace(glo.widthOfSlider); in scene 1 > my_mc > myNext_mc
    Is there a way so that I can first execute the code in scene 1 > my_mc > myNext_mc before the code in scene 1 > my_mc ?
    I am trying to get 725.45 through the trace(glo.widthOfSlider); in scene 1 > my_mc

  • Functional Global Variable in the CLAD sample Exam

    Hello,
    A question in the CLAD sample exam #2 keeps puzzling me. It's question number 32 about FGVs:
    32. Which is not an important part of creating a Functional Global Variable?
    a. Using Shift Registers to store information
    b. Changing the VI’s execution settings to Reentrant
    c. Setting the VI to inline into calling VIs
    d. Setting the While Loop to stop after one iteration
    The answer given is the following
    32.Correct Answer: B
    Topic: Functional Global Variables
    Justification: It is not necessary to inline functional global variables into their calling VIs. In fact, inlining requires that the subVI be reentrant, which is forbidden for functional global variables.
    Clearly, for an FGV to work properly, the VI must NOT be reentrant. So I would have selected answer B, but the justification seems to clearly point to answer C as well, doesn't it? Is it a typo, a subtlety in the wording? I am stuck on this one!
    Solved!
    Go to Solution.

    Well, inlining requires reentrant.  Therefore, the best answer should technically be C.  This looks like one of those rejected/retired questions since it isn't quite right and/or left up to too much interpretation.
    There are only two ways to tell somebody thanks: Kudos and Marked Solutions
    Unofficial Forum Rules and Guidelines

  • Using global variable in package

    Hi. I have created a function (Retrieve_SerialNo) which returns a variable, which I use throughout my package. I would like to assign this variable as a global variable to be used by all functions and procedures in the package. Can someone help me in the declaration of this variable as a global variable? Also, is it necessary for me to initialize this variable whenever the package executes. If yes, how would I do this?
    CREATE OR REPLACE PACKAGE BODY Supply_Item_Interface AS
    FUNCTION Retrieve_SerialNo RETURN VARCHAR2 IS
        v_serial_no VARCHAR2(20);
        CURSOR Serial_Code IS
          SELECT S.Serial_Code
            FROM Spare_Parts s, Orders r
           WHERE s.serial_code = r.serial_code;
      BEGIN
        OPEN Serial_Code;
        LOOP
          FETCH Serial_Code
            INTO v_serial_no;
          EXIT WHEN Serial_Code%NOTFOUND;
          v_serial_no := v_serial_no;
        END LOOP;
        CLOSE Serial_Code;
        RETURN v_serial_no;
      EXCEPTION
        WHEN OTHERS THEN
          RETURN NULL;
      END;

    user13415143 wrote:
    Hi. I have created a function (Retrieve_SerialNo) which returns a variable, which I use throughout my package. I would like to assign this variable as a global variable to be used by all functions and procedures in the package.All variables have scope or "visibility". A variable defined in a procedure is only visible within that procedure.
    A variable defines in a package body. is visible within that package body (i.e. procedures and functions in that package body can "see" that variable.
    A variable defined in the package definition? Well, who can see the definitions of procedures and function in a a package header/definition? Everyone else basically (other PL/SQL packages and procedures and functions). So this is also true for variables defined in the package interface. These are global variables that not only can be used by the code in that package's body, but also can be used by other packages and PL/SQL code.
    So when you create a global variable you need to decide on its scope:
    - define it in package header for global usage in all PL/SQL code
    - define it in package body for global usage within that package only
    CREATE OR REPLACE PACKAGE BODY Supply_Item_Interface AS
    ..snipped..Ugly code as there is no need to use an explicit cursor if returning a value from a single row. Also buggy code. If there are multiple rows returned by the cursor, the function returns the serial of the last random row. How does this make sense?
    This is what I would expect to see from a function like this. You pass it a unique identifier and it returns the applicable attribute (column) value for it.
    E.g.
    create or replace function GetSerialNo( orderNo number ) return number is
      serialNo number;
    begin
      select
        s.serial_code into serialNo
      from spare_parts s,
           orders o  
      where s.serial_code = o.serial_code
      and o.order_no = orderNo;
      return( serialNo );
    exception when NO_DATA_FOUND then
      return( null )
    end;Also note that there is no need to write ugly uppercase code. This is not a proper coding standard. Programming standards for all languages (ranging from C# to Java to Delphi to Visual Basic to C/C++) specify that camelcase should be used for variables and pascalcase for procedures/functions/methods. Uppercase is very seldom used and then only for constant names and compiler options/flags for example.
    Coding reserved words in uppercase? That is just plain silly - and not found in today's programming languages. Do yourself a favour and forget the idiotic standards used by some for PL/SQL and look at the standards for Java and .Net/C# - as the latter are the de facto standards for programming (and have been for the last 2 decades and more).

  • How to build labview global variable into dll?And how to use it in vc++ program?

    Hi!
       I want to build labview application into dll and use vc++ to call it.The labview program is a little complex,for it has many interface to vc++ and has while loop in it.When I use vc++ to call it,I must use vc++ to do other things.That is to say,vc++ creates a new thread to provide for the labview dll to run.the vc main thread goes on to other things.But the vc++ main thread must communicate with the labview dll by setting its inputs' parameters and get the results of running labview dll.Can you advise me how to realize it?
       I think global variable of labview could be useful when realizing the communication betweeb vc thread and labview dll.So I want to ask whether the labview global variable could also be built into dll and use it.Could you please tell me how to realize my idea?
       Thank you!

    [email protected] wrote:
    Hi!
    I want to build labview application into dll and use vc++ to call
    it.The labview program is a little complex,for it has many interface to
    vc++ and has while loop in it.When I use vc++ to call it,I must use
    vc++ to do other things.That is to say,vc++ creates a new thread to
    provide for the labview dll to run.the vc main thread goes on to other
    things.But the vc++ main thread must communicate with the labview dll
    by setting its inputs' parameters and get the results of running
    labview dll.Can you advise me how to realize it?
       I
    think global variable of labview could be useful when realizing the
    communication betweeb vc thread and labview dll.So I want to ask
    whether the labview global variable could also be built into dll and
    use it.Could you please tell me how to realize my idea?
       Thank you!
    You
    can't access LabVIEW globals directly from a caller to the LabVIEW DLL.
    However there is no problem in providing specific accessor VI functions
    to that global and export them as additional functions from the DLL.
    Rolf Kalbermatter
    Rolf Kalbermatter
    CIT Engineering Netherlands
    a division of Test & Measurement Solutions

  • Using a global variable within a function

    Hi all,
    I'm trying to learn how to use global variables, but can't quite get it right:
    Im trying to use two buttons, named UpButton and DownButton to control one global variable, p1
    A text field, named "Value" displays p1.
    Here's my code:
    p1 = 0;
    ButtonClick("UpButton", p1, 100,"Value");
    ButtonClick("DownButton", p1,(-100),"Value");
    function ButtonClick(ButtonName,Var,Increment,TextToChange){
                        sym.$(ButtonName).click(function(){
                        Var = Var + Increment;
                        sym.$(TextToChange).html(Var);
    However, it seems to be treating p1 as two different variables.
    Here's a link to the page to show you what I mean, apologies but this link wont work in google chrome because I'm using dropbox as a server temporarily
    In other browsers you may need to click "Show all content" or similar to any security warnings...
    https://dl.dropboxusercontent.com/u/83693404/ButtonTest/buttons.html
    Here are the project files:
    https://app.box.com/s/0shocivto8fl295h62uq
    Any help greatly appreciated, sorry if this is a stupid question,
    Katherine

    Hi Katherine,
    However, it seems to be treating p1 as two different variables.
    Indeed, your code created two different variables in two different scopes (I guess it as to do with JavaScript closures, but do  not ask me more, I am still a bit foggy about that idiosyncrasy ).
    In JavaScript, a primitive parameter – this is the case here with p1, a Number value –, is passed by value. In other words, a copy of the value is made. Your code handles two copies of the value stored in p1.
    This contrasts with an object parameter, which is passed by reference (address in memory), without copy. Your code would work if Numbers were passed by reference : the two Var (p1) would then point to the same address.
    The intent behind your trial is a global variable.
    1) Let us be as simple as possible :
    Stage : document.compositionReady event handler
    p1 = 0;
    buttonClick = function( Increment)
      p1 += Increment;
      sym.$( "Value").html( p1);
    Stage : DownButton.click event handler
    buttonClick(-100);
    Stage : UpButton.click event handler
    buttonClick(100);
    Without being preceded by the var keyword the variables are global.
    So the Number variable p1 can be accessed inside function buttonClick.
    And the Function variable buttonClick as well, is accessible inside click event handlers, everything (function definition +function calls) being inside the same symbol (Stage).
    2) Now, suppose this is no longer the case : you want to access a variable from another symbol.
    We create a new GraySquare symbol, instantiated both in the DownButton symbol (instance name DownSquare) and in the UpButton symbol (instance name DownSquare).
    Stage : document.compositionReady event handler
    p1 = 0;
    sym.buttonClick = function( Increment)
      p1 += Increment;
      sym.$( "Value").html( p1);
    The sym. prefix is now necessary to make the variable (here a Function, but you would proceed exactly the same with a String, Number or Boolean) accessible in other symbols.
    DownButton symbol : DownSquare.click event handler
    sym.getComposition().getStage().buttonClick( -100);
    UpButton symbol : UpSquare.click event handler
    sym.getComposition().getStage().buttonClick( 100);
    From these other symbols, the sym.getComposition().getStage(). prefix is necessary to acces to our global variable (function).
    The two examples are downloadable here : https://app.box.com/s/6vkyiqk7i8zwlw0j1wk1
    Gil

Maybe you are looking for