Unequal string copy

[bernie_carlton]

I'm using Compactlogix and RSLogix5000.

The external equipment vendor has a defined string shorter than the standard one (64 character versus 82 characters).

If a COPY is done from a shorter string to a standard string the last 18 characters of the standard string will probably end up as garbage.

Do subsequent string commands look at characters beyond those defined by the .LEN value or should I specifically null out the last 18 characters of the standard string just to be sure?

 

[nhatsen]

According to TN 50650 Custom STRING data types and copy to/from standard STRING tags (Access Level TechConnect) is possible to copy characters back and forth.

However, you're right about the garbage at the end of the string. I did a little test on Emulate and the COP instruction doesn't clear the longer string before copying the data from the shorter one. If you inspect the DATA array you will see some garbage at the end.

I think you can copy an empty string to your destination strings before executing another COP instructions involving short strings.

 

[bernie_carlton]

Actually I've decided to COPY an 18 element SINT array (all set to 0) into the final 18 character positions immediately after the string copy. It's only one place in the program so fine.

The 'garbage' would be whatever is in the 18 SINTs (4 1/2 DINTS - whatever) following the shorter string in memory.

And thanks for the Knowledgebase pointer. But copying an empty string in BEFORE the short -> standard copy is rather useless. The cleanup has to occur AFTER the string copy.