topic Re: How to set a flag in LabVIEW

How to set a flag

schorsche — Thu, 08 Jul 2004 11:16:15 GMT

How can I set a flag?
I tried to connect a boolean (true) to a local variable, but it didn't work since the local variable had a question mark in it!
Is there a better method to set a flag?

Many Thaanks

Re: How to set a flag

Ram2003 — Thu, 08 Jul 2004 12:08:51 GMT

You have created a local variable but not selected the Front Panel object. The way you do that is to right click the local variable you created and select the object you want to set flag.

Re: How to set a flag

schorsche — Thu, 08 Jul 2004 14:00:03 GMT

But I don't need a front panel object. I just wanna set a flag in the block diagram and retrieve its value at some other point in the program. So no front panel activity will be involved with it. The local variable shouldn't be linked with anything, all it should so is store a value!

Re: How to set a flag

Ram2003 — Thu, 08 Jul 2004 14:53:36 GMT

I saw you mentioning about local variables with a question mark, that is the reason for my response.
The way you can set a flag in the block diagram will be to use LabVIEW 2 style variables, where you will use a shift register to retain the flag value.

You cannot have a local variable without assigning any FP object.

Re: How to set a flag

Dennis_Knutson — Thu, 08 Jul 2004 15:11:23 GMT

Why don't you just use a wire or shift register to pass a value? That's the prefered method in LabVIEW. A local or global (LV2 style or not) should be considered as a last resort.

Re: How to set a flag

schorsche — Thu, 08 Jul 2004 22:24:16 GMT

...Hello,

I'm using quite many local variables. I think that keeps the block diagram tidy, rather than having a ton of for/while loops with shift registers instead.

Cheerio

Re: How to set a flag

Dennis_Knutson — Fri, 09 Jul 2004 13:08:40 GMT

They also use extra memory which can also dramatically slow down your app and they break dataflow with the risk of race conditions. Programs with a lot of locals are much harder to debug - trust me on this. Shift registers can be very tidy if done right and don't cause the problems that locals do. The "LabVIEW Development Guidelines" document that ships with LabVIEW has a section on locals/globals and a reference to functional global variables which can be used to replace a standard global variable but nothing in LabVIEW is as effecient as a wire.

Re: How to set a flag

Steven Bird — Mon, 12 Jul 2004 11:08:55 GMT

Totally Agree Dennis, limit the use of Local variables and take caution when using them in communicating data between parts of your code.

In your initial comment regarding local varibles, create a front panel object then set the hide property so you cant see the object.

Kind Regards

Steven Bird
Applications Engineer
National Instruments

Re: How to set a flag

FLiu — Mon, 05 Oct 2015 18:55:48 GMT

Hi Dennis_Knutson

I am developing a calibration application for multiple sensors. large amount of attributes such as build code, matrix code, ranges, sensor types, etc need to be throughly checked and passed to each sensor through serial communication. I used a lot of local variables on the home screen and it indeed slows down the system. I was thinking to create a lookup table using variants and save all the attributes for each sensor. That way I can conveniently log, retrieve and pass to DUT. What are your thoughts.

Thanks

FLiu

Re: How to set a flag

Hooovahh — Mon, 05 Oct 2015 19:38:39 GMT

@FLiu wrote:

What are your thoughts.

Probably that a lot has changed in 11 year, and that a new thread should be made where you clearly explain your issues, posting details and example code.

11 years ago a 3 mega pixel camera cost about $200, and new cell phones had a 1 mega pixel camera.