Hello 0_Einstein.

For the first time I'm working on trying to create a code to empty a string (or an array of strings) with null characters and with 0 length.

I tried to use your code about the FC and for me it doesn't work.

This part of code inside the FC:

"BEGIN
in_str10 := "ConstantsDB".Null_str10;  // fill with null characters
in_str10 := ''; // set the actual length = 0
END
"

is different from this part of code:

Inside the FC "in_str10" is an in/out parameter of the FC and what I look and simulate is that the parameter is updated only at the end of the FC so only the last instruction is executed and the string remain with the privious elements with 0 length. If you reverse the order of the code the string is fill with 10 elements null and the length is 10.

Put the "same" code outside of the FC works because the first instruction is executed and completed (filling the string with null elements) and after the other is executed and completed (setting the length of the string to 0).

Inside the FC is necessary to put a delay (or make 2 execution cycles) where on the first cycle the string if fill with null characters and on the second one is set to 0 length.

For me the problem remain the same if the string is defined with a fixed number of characters or it is defined like a pointer (254 + 2 byte occupied).

At the moment I didn't find any other solution different to this:

1) create an FC to fill the string with null characters (or making a S_MOVE of a string with all null elements)

2) create an FC to set the length of the string to 0 (or making a S_MOVE of ''

So if I need to copy one string ("input string") to another ("output string") and reset the first one (like making a "tracking" of a code  I am "forced" to do this:

1) fill the "output string" with null characters

2) copy the "input string" to "output string" (characters and length are correctly updated)

3) fill the "input string" with null characters

4) set the length of the "input string" to 0

For me this one isn't an "compact" solution to make a copy and empty a string that works in any case.

Has anyone already found a more efficient solution than mine? If so please share it.

Thanks.

Franco

------------------------------------------------------------------------------------------
Split from Need to delete all the string elements of an array [1..30].

Hello 0_Einstein.

Thanks for your unswer.

It's not important if your recommendation is from 2021. I am not able to make it working. Maybe I am making a mistake somewhere but I don't know where.

The problem is not on this part:

"

If you have a DB with that tag name and tag datatype (of the UDT named str10), then the assignment of 10 null characters to a tag of UDT datatype str10 will fill it with null characters and set the length to 10.

The next part is to set the tag to "" to set the str10 tag length to 0, but inside the bytes of that same str10 tag are all $0 (null character).

What is not working?

"

This part is working.

For me this part doesn't work:

"

FC_Set_str10_All_To_Null
IN_OUT:
in_str10 : str10
END

BEGIN
in_str10 := "ConstantsDB".Null_str10;  // fill with null characters
in_str10 := ""; // set the actual length = 0
END

"

If you create an FC with this configuration (in/out parameter) it doesn't work as we espect so fill the string with null characters and set it with length 0 (and it is what I need) but only set its length to 0 without filling the string to null characters because only the last instruction is executed when it makes the update of the out parameter at the end of the FC (my opinion). The Plc simulation of that FC says this. In fact if you reverse the order of the instructions the string is fill with null characters without setting its length to 0.

The behaviour of that FC (i hope that it is equal to yours, names are different but the concept is the same) is different from put the code:

"

"

for the reasons that I wrote on my privious comment. In fact I created different FCs that basically creplicate the behaviour of the above code as I wrote under. They works properly but what I want to understand is if someone has already found a solution more efficient than mine. This because to make a transfer from one string to another and delete the first one I have to call 3 FCs and make a S_MOVE. Not so efficient for my point of view.

On my opinion S_MOVE should work in different way and when you make a move of the string it should make an exact copy of the string on the output string and not only copy its characters (so if the output string previously had more characters the final result is a mix of the input string with the remain output string characters not overwritten. Furthermore in this way the actual length of the output string is set equal to the length of the input string that can be not true in all the cases.

And it shoud be preset an instruction like S_DELETE that make with one instruction a complete delete of the string (with null characters and length 0) non related to how the string is configured (Xx elements or pointer).

If you can try to simulate your FC and tell me if it works or not. If so please update with the export of the source code of all the elements required.

Thanks.

Franco

0_Einstein

So, my recommendation from 2021 is not sufficient for your needs, or you are not able to make it work?

Did you create a UDT and DB as follows:

User Data Types:
str10 : string[10]

ConstantsDB:
Null_str10 : str10 : Default: $0$0$0$0$0$0$0$0$0$0

If you have a DB with that tag name and tag datatype (of the UDT named str10), then the assignment of 10 null characters to a tag of UDT datatype str10 will fill it with null characters and set the length to 10.

The next part is to set the tag to "" to set the str10 tag length to 0, but inside the bytes of that same str10 tag are all $0 (null character).

What is not working?

Is it because you are using an In_Out tag for the str10 in your FC it does not work, or something else? 

FrankyMagician

Hello 0_Einstein.

For the first time I'm working on trying to create a code to empty a string (or an array of strings) with null characters and with 0 length.

I tried to use your code about the FC and for me it doesn't work.

This part of code inside the FC:

"BEGIN
in_str10 := "ConstantsDB".Null_str10;  // fill with null characters
in_str10 := ''; // set the actual length = 0
END
"

is different from this part of code:

some_str10 := "ConstantsDB".Null_str10;

some_str10 := "";

Inside the FC "in_str10" is an in/out parameter of the FC and what I look and simulate is that the parameter is updated only at the end of the FC so only the last instruction is executed and the string remain with the privious elements with 0 length. If you reverse the order of the code the string is fill with 10 elements null and the length is 10.

Put the "same" code outside of the FC works because the first instruction is executed and completed (filling the string with null elements) and after the other is executed and completed (setting the length of the string to 0).

Inside the FC is necessary to put a delay (or make 2 execution cycles) where on the first cycle the string if fill with null characters and on the second one is set to 0 length.

For me the problem remain the same if the string is defined with a fixed number of characters or it is defined like a pointer (254 + 2 byte occupied).

At the moment I didn't find any other solution different to this:

1) create an FC to fill the string with null characters (or making a S_MOVE of a string with all null elements)

2) create an FC to set the length of the string to 0 (or making a S_MOVE of ''

So if I need to copy one string ("input string") to another ("output string") and reset the first one (like making a "tracking" of a code  I am "forced" to do this:

1) fill the "output string" with null characters

2) copy the "input string" to "output string" (characters and length are correctly updated)

3) fill the "input string" with null characters

4) set the length of the "input string" to 0

For me this one isn't an "compact" solution to make a copy and empty a string that works in any case.

Has anyone already found a more efficient solution than mine? If so please share it.

Thanks.

Franco

 

Hello qwazee.

Sorry for my long privious posts but I tried to explain better as I can what was my problem and what is my solution that I don't know if if is "optimized".

I answer to your questions.

"why it is important for you to have the unused characters set to a zero character?"

Because I have a system that read the complete string (in my case 254 characters). And I built a system that makes a tracking of a code (string of 254 characters) that moves the code from one zone to another when the product really moves from one zone to another. So I don't need to have two strings with the same content but move one string to another and delete completely the privious one. How can I make it efficiently this thing?

"To make an exact copy of one STRING to another would need to use non optimized data using the a type of raw copy command."

What do you mean with this? Explain me better with code please.

Thanks.

Franco