Local variable versus 'properity value'

Hi,
can anybody explain me the (dis-)advantages of using 'properity:value'
instead of using a local variable when I want to read (write) a control
at a second location.
Thanks for any input
Urs Bögli

First : Greetings from another "Bögli" on the Developer Exchange.
I don't think there are other issues. But, like Dan said, the property node will be much slower. This is because it will force LV to switch to the user interface every time you read the property.
I have just made a little test to give you some figures. Simple for loop with 1000000 iterations in which the value is read.
Local variable = 15 times slower than Terminal
Property node = 653 (!!!) times slower than Terminal
If performance is an issue, the property node is not the way to go !

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Sun Sudio C++: Local Variables and Watches Values Not Initialized in Debug

Hi All,
I am trying to debug my program (using dbx). I have put break points in various functions. However, I have the following problems:
- when the program runs to the break points, all arguments have in the functions shown in the callstack have values '???';
- NOTHING is shown in the 'Local Variables' windows;
- if I put the local variables in the 'Watches' window, the 'value' simply says <unset value>;
what am I doing wrong?
Thanks in advance

Well, first things that comes to my mind is that your app was not compiled with debug info. Could you please post output of the following three commands here:
$ dwarfdump -l <your app> | wc -l
$ dumpstabs -s <your app> | wc -l
$ file <your app>
(if the first two would print small number, remove "wc -l" and post real output here, please)

Local Variables Versus Global Variables

DATA A TYPE I VALUE 100.
PERFORM PRINT_DATA.
FORM PRINT_DATA.
           DATA A(10) TYPE C 'HELLO'.
           WRITE / A. "Wanted to Print 100 (Global)
           WRITE / A. "Wanted to Print 'HELLO'(Local)
ENDFORM.
Note : Both the times, the Local Variable 'A' is Printed .
?Is there any way to   Differentiate the Local and Global Variables When the Names Are Same.*
*It Might be Possible in Object Oriented But I am Looking for the Same in FORMs.

Hello Gagan,
You want to print the Global as well as the local values of the variable named "A". Here are a couple of approaches:
1.The 'Subroutines' are part of the modularization techniques. There are certain keywords like "using" & "Changing" so that you can work by passing Values.
2. There is a keyword named "LOCAL". Declare data object with the keyword "LOCAL" and then try the 'write" statement. I suppose this should work for you.
Let me know if any one of the above works or if you need more help.
Best Regards,
Chaitanya

Local variables vs property knots- value

What is the advantage of local variables versus property knots (value)?
They tell in the manual, that for every local variable there is always a copy made of the original
input/indicator. If i use the property knots (value) no copy is made.
So what is the use of local variables?
Which methods exits else to avoid too long wires?
Sneff

As Mike already told you, you should try to avoid variables (both locals and globals) just as usage of property nodes value. There are several reasons for this:
- Bad diagram design with variables
- Trying to work around a bad architecture by using variables instead of switching to a fitting one
- race conditions (insecure datamanagement)
- performanceissues
Besides that, using variables vs propety nodes (value) are the following:
- property nodes are always executed in the UI thread => slow
- variables as well as the property node copy the data of the control\indicator in case of reading => exposed, well, predestinated for race conditions
hope this helps,
Norbert
CEO: What exactly is stopping us from doing this?
Expert: Geometry
Marketing Manager: Just ignore it.

How many ways to read and write a local variable in a called VI?

Ciao!
I'm producing my first TestStand sequence. It is called "FirstAttempt" and it is made by a single step which calls a VI. One of the first dilemmas i encountered realizing this sequence is how to read and write a local variable (created going in Variables -> Locals ('FirstAttempt') -> <right click to insert local>) in the called VI.
The first way (the only one i tried) is to create a control and an indicator on the VI front panel, connect them to their respective terminals in the connector pane and then specify (going in Step Settings -> Module) that these connectors (shown in the Parameter Name column) are linked to the local variable (selected in the Value column).
The second way (not tried) consists in using TestStand API: create a Sequence Context reference on the VI front panel, link it to a property node in the block diagram, select the property "Locals" and extract from this the local variable name and value which, i think, can be readable and writable.
So...
Are the shown ways correct?
Are there other ways?
Knowing that a "local" variable can be considered "global" within the whole sequence, is there the possibility to simply create a reference to the local variable and use the reference in the called VI block diagram in order to save space in the connector pane (if using method 1) or in the block diagram (if using method 2)?
Thanks!
Message Edited by aRCo on 09-17-2009 05:09 AM

Hi,
Before TestStand 3 you would use the second way you quoted as its the only way.
But now you would use the first way you quoted. You may still what to pass the SequenceContext if you were going to use the TestStand API. For TestStand 3.x and above you would use this way as the first chose. (Personnelly, I would not pass the SequenceContext into a VI if I know it was never going to be used in that VI.)
Not sure I understand your final comment, maybe you are liking it to passing the reference of a control to a subVI so that the control can be updated from within the subVI.
If this is the case and you had a situation where you had a step that was running in parallel with the rest of the steps in the sequence either as a separate thread or execution and were dependent on the contents of the local variable changing from that parallel running step, then you would have to use the API SetVal method to change the local.
Hope this is clear.
Regards
Ray Farmer
Regards
Ray Farmer

How to change value of instance variable and local variable at run time?

As we can change value at run time using debug mode of Eclipse. I want to do this by using a standalone prgram from where I can change the value of a variable at runtime.
Suppose I have a class, say employee like -
class employee {
public String name;
employee(String name){
this.name = name;
public int showSalary(){
int salary = 10000;
return salary;
public String showName()
return name;
i want to change the value of instance variable "name" and local variable "salary" from a stand alone program?
My standalone program will not use employee class; i mean not creating any instance or extending it. This is being used by any other calss in project.
Can someone tell me how to change these value?
Please help
Regards,
Sujeet Sharma

This is the tutorial You should interest in. According to 'name' field of the class, it's value can be change with reflection. I'm not sure if local variable ('salary') can be changed - rather not.

Inserting in the UUT_Results table a value that we read from our data base from a local variable

We would like to include in the UUT_Results table a value that we read from our data base into a local variable during the execution of our sequence file. We found that by modifying the configure database options we were able to add a column for this variable, but the local variable was not available to be placed into an expression for that column from the local variables or parameters. Is it possible to do this, and if so, how? Station Globals were available to be included in the expression, however the sequence file may be executed on more than one system which makes the Global unavailable on systems other than the one where the sequence file originated.

You can use the TestStand API to programmatically create global variables at runtime, thus ensuring their existence. For example, you could call Engine.Globals.SetValString("GlobalStringVariableName", PropOption_InsertIfMissing, "variable value")
Of course, if you need to test multiple UUTs in parallel, a single global is not sufficient. In that case you might consider adding the field you need to the UUT datatype in the process model. You could then access the field in your sequence via RunState.Root.Locals.UUT.YourNewField = YourNewValue.
If you also want your sequence to run without using a process model, you must check for the existence of the UUT before accessing it. You could use the expression function: PropertyExists("RunState.Root.Locals.UUT.YourNewFi
eld")

Error in assigning value to local variable

i am writing a stored procedure in which i have pass parameter if parameter value is zero then i assign a previously declared variable null else that value
syntax is this
create or replace
PROCEDURE usp_Add_Update_Insurance
p_CityID IN NUMBER DEFAULT NULL
as
v_CityID number(10,0);
begin
IF p_CityID = 0 THEN
BEGIN
v_CityID := NULL;-----giving error in this line
else
v_CityID:=p_CityID;
END;
END IF;
end
begin
///some query
end
please help someone

I think there is no added value by putting those Begin/End.
The simplest solution is just remove them
Create Or Replace
Procedure Usp_Add_Update_Insurance (
     P_Cityid In Number Default Null
) As
     V_Cityid Number(10,0);
Begin
     If P_Cityid = 0 Then
          V_Cityid := Null;
     Else
          V_Cityid:=P_Cityid;
     End If;
     -- do something with V_Cityid
End; The only reason for having Begin/End is if you want to catch some exceptions or perform some strange local variable declarations. But it does not seems to be case here.
MJ

How to assign bean value to a local variable in JSP using struts.

Hi everybody!
I've a problem that puzzled me on how to assign a bean value to a local variable like String in JSP using struts.
we can have someting like this to display the value
<bean:write name="detailService" property="status" />or
<bean:define id="theStatus" name="detailService" property="status"/>
This is country: <%=theStatus%>but an error occured when I tried like this:
String currentStatus = "<bean:define id="theStatus" name="detailService" property="status"/>";
or
String currentStatus = "<bean:write name="detailService" property="status" />";Is there a way to do this?.....
Any help pretty much appreciated

Java != JSP.
The <bean:define> and <bean:write> tags are custom tags meant to appear in the HTML section of a JSP file, as opposed to the scriptlet section. They actually get turned into java code as part of the translation process.
The <bean:write> tag naturally just writes out what you tell it to.
The <bean:define> tag defines a local variable, and gives it a value.
this should do it.
<bean:define id="theStatus" name="detailService" property="status" type="java.lang.String"/>
<%
String currentStatus = theStatus;
%>With the advent of JSTL, you shouldn't really need to use scriptlet code anymore. Personally I am for 0% scriptlet code in any jsp I write.

How come my local variable is not updating it's value with respect to what's happening in the while loop?

Hello,
I am trying to extract data out of a while loop as my declarations update with respect to the iteration number. I have attempted to use both local variables and shift registers, but with no luck.
I have also done the following example: http://www.ni.com/white-paper/7585/en and it works like a charm.
I attached the PNG file with local variable declaration circled in red. Will attach a VI in the next respnose.
Thanks
Solved!
Go to Solution.
Attachments:
Local Variable.png ‏366 KB

OK, looking at the code...
Can you explain what it is supposed to do? What's the purpose of the value property node read which only seems to update an indicator.
The inner while loop should proably be a FOR loop, because the number of iterations is known before the loop starts.
Your use of formula nodes seems overly complicated.
LabVIEW Champion . Do more with less code and in less time .

How to set multple values in cluster with local variable?

Hello all,
Ok, I've made my way through Labview for everyone, and have some basic concepts down. I can see with a cluster, if acting directly upon it, you can unbundle, change values, rebundle, etc.
I'm trying something a bit more complex...and just not sure how to get started on this.
I have a drop down menu ring. I have set this up as a typedef, with 4 values. I have used this typedef 7 times, plus some LED bools, in a cluster. I have made this cluster a typedef.
So, in my main vi I"m starting to design, I've set up an example posted here....and in it, I have two instantiations of the cluster typedef, Left Selector and Right Selector.
I have dropped into this vi, a copy of the menu ring typedef (same typedef as in the clusters, same values)....called reset all tubes.
I'm trying now, to figure out how, with an event on the change of value for 'reset all tubes'....that I can start with the left selector, and change all the tubes (these are the menu ring selector) to the same value as what has been selected with the 'reset all tubes' menu ring.
I've created a local variable for the left selector. It is set to read values. (I'll be doing the same with the right one too, but just starting with the left).
In examples I've seen where directly accessing a cluster, you could unbundle the cluster...loop through and change the values...maybe pull out all of the 'tubes' into an array and move through that to update the values. And when you bundle or unbundle the cluster...you can see the values, etc, when you stretch them out on the block diagram.
With the local variable..I can't see to 'stretch' it out like I was expecting..so I can access the values for the 'tubes'...and set them all to the value of the 'reset all tubes' ring menu value.
Can someone put me on the path on the best way to do this....or is there a structure of component I'm missing here ? Am I on the right track to begin with here?
This would seem pretty basic to me, but I'm just missing something here on how to start...
Thank you in advance,
cayenne
Solved!
Go to Solution.
Attachments:
example_select_dropdown.ctl ‏5 KB
public_selector_cluster.ctl ‏6 KB
laptop_test_public.vi ‏12 KB

nathand wrote:
You can't do this with a for loop the way the cluster is structured, but why make it so complicated? Just bundle the new value into the cluster as shown below:
If you do want to use a for loop, consider restructuring your cluster. Group the ring and a boolean into a cluster, then drop 7 of those into the selector cluster. Then you can use "cluster to array" and "array to cluster" since all elements in the outer cluster will be of the same type.
Also, be careful using rings as type definitions. You probably want to use an enumeration instead. The items in a ring do not update when you update the type definition because they're considered to be cosmetic; the items in an enumeration type definition do update, because the items in an enumeration are considered part of the data type.
Oh my goodness!!
What was MUCH easier than I was trying to make it!!
I was attempting to do this reset, in an incremental fashion, as that later, I'm going to need to change values in this cluster by individual elements....and was using this as a way to try to understand how to iterate between cluster elements, and change the values of each one.
This solution works much better for this 'reset' all solution.
One question on this....with regard to the enum vs the ring menu.
I was actually going to go with the enum, however, I could not find a way to make it LOOK like the ring menu...with the arrow to the side that a user would know to click to present the menu list of choices.
I see with the enum, that you can remove the increment/decrement indicator.....and if the user clicks the control, it will indeed pop up a menu of choices...but there is no 'arrow' on that control to indicate to the user that it is a menu choice there.....
Is there a way to make and enum look like a ring with the "drop down menu" control look?
Again, thank you !!
This helps!
C

Best way to get the values of local variables

What is currently the best way to get the values of local variables. I know it is not currently possible to set watchpoints on local variables, but what are the best workarounds?

You have to use StackFrame methods, eg, visibleVariables and getValues. To get a StackFrame for a thread, that thread has to be suspended, eg, by a BreakpointEvent.

Local variable default value

Hi
Just a quick question to get me out of a hole..... I am using local variable to control while loops, and based on a counter value, it turns it on or off. When i probe the value of the actual boolean, it comes up not exectuted, but the local indicator value is true???? is there any way to change this?? i need to to remain false, UNTIL it goes true!
Cheers
Peter
Solved!
Go to Solution.

I think that "Ravens" has hit the nail on the head. Using unprotected shared resources (like local variables) in parallel will open the door to race conditions... the bane of any programmers life!
Here are some useful resources which further explain this concept.
Using a Local, Global, or Shared Variable in Parallel Loops Can Cause Race Conditions
http://digital.ni.com/public.nsf/allkb/4F3CC921B4179F9F86256A3B0045CE2D
Tutorial: Local Variable, Global Variable, and Race Conditions
http://zone.ni.com/devzone/cda/tut/p/id/7585
The first link also mentions the producer/consumer articeture and the semaphore. Both great solutions. However, correctly sequencing your source code (using things like error clusters) will help prevent this issue.
Further more, I wonder if you are initialising your variables??
You should write a value of false to the variable before you enter the main body of your code. This ensure that the first time you read from the variable it will return a known value (false). If you dont do this, the variable will return what ever was the last value written to it.
Hope this has been useful.
Rich R
Applications Engineer
National Instruments UK & Ireland

Is This a Global Versus Local Variable Problem?

I intend to use a variable (myselector) with a text value (e.g. roses, Big Sur, Pacific Grove, night, etc.) for the sort criteria of my photography list. Selection of a tab from a Tabbed Panel will appropriately define the variable and the selected thumbnails will display in the Content Panel.
The variable "myselector" is defined in the head section; a function for each tab of the Tabbed Panel will redefine the variable per the selected tab. Within the function, I am not using "var" to call the variable. Though the variable "myselector" should be global, the changes to its value are discarded when the function closes. This indicates that it is functioning like a local variable in the function. After a bit of reading, I've not found the cause of the global/local discrepancy or a fix for it.
Diagnosis History - I generated a simplified code. Variable "myselector" is defined as "abcd"; function "myfilter" is called by onclick of the text "button" and changes "myselector" to "efgh". At the end of the file, I used "document.write (myselector) to output the "myselector" value. The script follows.
The end value of "myselector" does not change. However, when I add "document.write (myselector)" to the function, then the changed value is displayed.
I ask someone to explain what I am doing incorrectly or, at least, guide me to a solution. I thank you for your assistance.
Scott
<script type="text/javascript">
var myselector="abcd";
function MM_callJS(jsStr) { //v2.0
return eval(jsStr)
</script>
</head>
<body>
<div id=text>
<p onclick="MM_callJS('myfilter();')">Button</p>
<script type="text/javascript">
function myfilter() {myselector="efgh"; }
</script>
<script type="text/javascript">
document.write (myselector);
</script>
</div>

Dear Ben:
I thank youfor your patience. This includes the script using Insert - Syntax Highlighting - Java.
The coding needs a lot of clean up but I want it to work, first.
Scott
<script src="SpryAssets/xpath.js" type="text/javascript"></script>
<script src="SpryAssets/SpryData.js" type="text/javascript"></script>
<script src="SpryAssets/SpryTabbedPanels.js" type="text/javascript"></script>
<script type="text/javascript">
var dsphotodata = new Spry.Data.XMLDataSet("EM_photo.xml", "/gallery");
</script>
<script type = "text/javascript">
function MM_callJS(jsStr) { //v2.0
return eval(jsStr)
</script>
<script type="text/javascript">
var dsphoto = new Spry.Data.XMLDataSet("EM_photo.xml", "/gallery/photos/photo");
dsphoto.filter(subjectfilter);
var myselector;
</script>
<link href="SpryAssets/SpryTabbedPanels.css" rel="stylesheet" type="text/css" />
</head>
<body>
This is a test of Scott's efforts to program his website.
<br />
<br />
<div id="TabbedPanels1" class="TabbedPanels">
<ul class="TabbedPanelsTabGroup">
    <li class="TabbedPanelsTab" tabindex="0" onclick="MM_callJS('{myselector=\'animal\'}; subjectfilter(); dsphoto.filter(subjectfilter); ')">Tab 1</li>
    <li class="TabbedPanelsTab" tabindex="0" onfocus="MM_callJS('myselector=\"pgbeach\" subjectfilter(); dsphoto.filter(subjectfilter); ')">Tab 2</li>
    <li class="TabbedPanelsTab" tabindex="0">Blank</li>
</ul>
<div class="TabbedPanelsContentGroup">
    <div class="TabbedPanelsContent" >Content 1
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<br />
<script> {document.write (myselector)} </script>
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      <div spry:region="dsphoto dsphotodata"> <img src="{dsphotodata::thumbnail/@base}{@thumbpath}" width = {@thumbwidth}px height = {@thumbheight}px spry:repeat="dsphoto" onclick="dsphoto.setCurrentRow('{ds_RowID}');" /></div>
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    <div class="TabbedPanelsContent">Content 2
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      <br />
      <div spry:region="dsphoto dsphotodata"> <img src="{dsphotodata::thumbnail/@base}{@thumbpath}" width = {@thumbwidth}px height = {@thumbheight}px spry:repeat="dsphoto" onclick="dsphoto.setCurrentRow('{ds_RowID}');" /></div>
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<div spry:region="dsphoto dsphotodata"> <img src="{dsphotodata::thumbnail/@base}{@thumbpath}" width = {@thumbwidth}px height = {@thumbheight}px spry:repeat="dsphoto" onclick="dsphoto.setCurrentRow('{ds_RowID}');" /></div>
</div>
</div>
</div>
<div id="Selected_Photo" spry:detailregion = "dsphoto dsphotodata" >
<img src="Photo-Thumbnails/{@thumbpath}" width = {@thumbwidth}px height = {@thumbheight}px /><br />
<img src="Photo-Email/{@path}" width = {@width}px height = {@height}px />
</div>
<script type="text/javascript">
var subjectfilter = function(dataSet, row, rowNumber, criteria) { if (row["@subject"].search (myselector) != -1) return row; return null; };

</script>

Unable to see local variable values when debugging java

Hi,
I am using JDev 10.1.2 with java version 1.4.2_04.
I have been using JDev to debug my java programs. But suddenly from this morning I am unable to see local variable values. I am able to see class and instance variables. This has happened to me before and I had restarted my machine couple of time, to get this sorted. But this time, nothing helps. Going thru the forum I found out that Include Debug information (Project Properties -> Compiler Option) need to be turned ON. It is already turned ON for me.
I would greatly appreciate if you could let me know how to crack this problem.
Thanks in advance.

No. The local variables 'used' to show up during debugging. But erratically it doesn't show up local variable values. I had to restart my machine couple of times whenever this happens, inorder to see the local variable values. But this time even restarting doesn't help.
Is there any preference setup that need to be turned on/off to see local variables?
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Local variable versus 'properity value'

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