Clearing Out a String Tag

recondaddy · May 17, 2006

Is there an instruction in RSLogix5000 for clearing out a string tag? I've tried COP with a zero as the source and the string tag as the destination with a length of 1. I get

"COP, Operand 0: Invalid kind (tag, literal, or expression) of operand."

I've also tried MOV with a zero as the source and the string tag as the destination. With that, I get

"MOV, Operand 1: Invalid type."

I can't really use DEL because I never know the exact number of characters that the string will contain.

Anyone have any guidance?

kamalaitounejjar · May 17, 2006

Try with CLR (clear instruction)
ex:
CLR my_string.DATA[0]

recondaddy · May 17, 2006

Yep. I figured it out. Didn't realize that you needed to write a zero to the .DATA[0] element of the string tag:

MOV
Source: 0
Dest: MyString[1].DATA[0]

Or, I guess a CLR would work just as well. Thanks for your help.

Doug-P · May 17, 2006

recondaddy said:
I've also tried MOV with a zero as the source and the string tag as the destination. With that, I get

"MOV, Operand 1: Invalid type."

The error message is telling you exactly what you're doing wrong, that is, trying to move a numeric value into a string. If you'd use a null string (string = "") as operand 1, I bet it would work.

Gerry · May 17, 2006

CLR or MOV will only clear one character. To clear all characters from the string use FLL.

FLL,0,string_tag.data[0],x

where x is the length of the string.

theColonel26 · Mar 17, 2020

Doug-P said:
"MOV, Operand 1: Invalid type."

The error message is telling you exactly what you're doing wrong, that is, trying to move a numeric value into a string. If you'd use a null string (string = "") as operand 1, I bet it would work.

How does one get a null string when there are no String Literals? Just a string that was never assigned anything

P.S. AB Sucks, Long Live IEC61113-3
P.P.S. I have to us AB

I hate it so much.

P.P.P.S. I was in High School when this thread was started...

Jeev · Mar 17, 2020

Gerry said:
FLL,0,string_tag.data[0],x

where x is the length of the string.

Adding to that you can use FLL with 0 as the source, the STRING as the destination, and 1 as the length. It will fill the LEN and every SINT with 0 and blow the whole lot away.

theColonel26 said:
How does one get a null string when there are no String Literals? Just a string that was never assigned anything

You make one. If you NEED a blank string, create gsBlank as a STRING, leave it empty, and then make it a constant.

Ken Roach · Mar 17, 2020

Adding to that you can use FLL with 0 as the source, the STRING as the destination, and 1 as the length.

:facepalm:

All this time (literally decades) I've been doing it the "hard" way by addressing both the LEN and DATA.

I think we might be seeing more zombie threads this week than usual. But hey, never too old to learn.

Jeev · Mar 17, 2020

Ken Roach said:
All this time (literally decades) I've been doing it the "hard" way by addressing both the LEN and DATA.

I have been working on so many serialisation projects over the last few years that doing things with strings that a PLC should never have to do has become commonplace

#Databases
#Industry4.0
#BigData

bernie_carlton · Mar 17, 2020

I always kept an empty string, tag name empty_string, and COPyed it to the target - length 1.

JeffKiper · Mar 18, 2020

Im with Bernie. I use a blank string and COP.,its probably not the most smallest use of memory but its easy and memory is cheap lately

theColonel26 · Mar 18, 2020

So apparently at least in v30+ this is perfectly valid......

Which means RS 5000 does have string literals.......

Which mean all these other hacks are useless.

bernie_carlton · Mar 18, 2020

I use an analogous method for clearing other UDTs, just keep a copy with appropriate initialization values.

BachPhi · Mar 18, 2020

Clearing an array of string

Clear one string is an easy part.
A little more challenging is clearing an array of string:

https://www.advancedhmi.com/forum/index.php?topic=2584.msg15541#msg15541

Jeev · Mar 18, 2020

BachPhi said:
Clear one string is an easy part.
A little more challenging is clearing an array of string:

https://www.advancedhmi.com/forum/index.php?topic=2584.msg15541#msg15541

Still works. FLL 0 ARRAY 1 - Done. It also works for Structures and UDT's.

Clearing Out a String Tag

recondaddy

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