Enlarging arrays?

Hi,

how would you enlarge an array?

I need to do a project with following visualization:
- text field, where user inputs data
- button, which user hits when he is done writing
- combo text field, which displays some data, and after the button is hit, value of text field is added to this data as new value (new cell of the array data)

User will be able to add data multiple times. Which means program must add a new cell to data array every time he hits the button. How do I accomplish that?

Regards,
shrimper

I'm not aware of any PLCs that can dynamically change the size of arrays without a program change. Memory allocation is,for the most part, static and "hard-wired" in the program. Generally you have to set an array size to the maximum that your application will require.

I've seen cases where programmers used arrays much larger than expected, and then separately tracked how many values were currently in the array. Everything unused was just left at the default empty/zero state.

Personally, I'm really glad that PLCs have statically assigned memory. Dynamic memory issues like memory leaks are at the heart of so many of the PC related problems we have.

I've done this using a DB as the backend for the data storage.

As jstolaruk says, PLC's can't dynamically change the size of the arrays at runtime. You have to just create them large enough to handle the maximum amount of data. My rule of thumb is "think of a number, and then double it"

Then you just have to deal with checking whether each array element is used or not, and checking if there are any spares and advising the operator if not. If you created a warning for say, only 5 array elements left, that should in most applications give you enough warning to schedule a download to increase the size of your array.

mk42 said:

I've seen cases where programmers used arrays much larger than expected, and then separately tracked how many values were currently in the array. Everything unused was just left at the default empty/zero state.

Click to expand...

Are they ever empty though after creation? An array[100] of DINTs with a value >0 in the first 5 and zero in the last 95 - will it take up the same memory as if they didn't contain the value zero?

janner_10 said:

Are they ever empty though after creation? An array[100] of DINTs with a value >0 in the first 5 and zero in the last 95 - will it take up the same memory as if they didn't contain the value zero?

Click to expand...

Yes...A value of 0 or XXXXXXX still takes the same amount of bytes of memory.

robertmee said:

Yes...A value of 0 or XXXXXXX still takes the same amount of bytes of memory.

Click to expand...

Agreed. I just meant "empty" as in "containing no useful data". Still takes up space.