Published: 15.05.2021 | Edited: 15.05.2021 | Tags: 100daystooffload

Unexpected naming conventions

In IEC 61131-3 compatible programming environments, string manipulation have many inbuilt functions. Unfortunately, sometimes the routines are a little bit hard to find. Even though it is possible to do a search through available functions, just searching by name sometimes won't cut it.

Searching around for a substring function with the terms string, substr or just sub returned no relevant results. Fortunately, we live in the world where the Internet is almost ever present and it is possible to reach for the knowledge stored there, provided, someone else had already shared it before.

To get the leftmost N characters, the function LEFT is used with the signature:

STRING LEFT(STRING STR, INT SIZE)

Subsequently, to get the rightmost N characters of the string, to for instance reduce four character year representation to the two characters, function RIGHT can be usued:

STRING RIGHT(STRING STR, INT SIZE)

To get the actual substring, it is possible to daisy-chain these two functions, cutting the string from the both sides. There is a however an even shorter way, called MID, meaning the function is returning the middle part of the string, or the substring:

STRING MID(STRING STR, INT LEN, INT POS)

I do not know who was creating these names, but in my mind, a middle is a point on the line having the same distance from both line's ends, which clearly is not the case for the MID function, as it starts at the given POSition an takes specified LENght of characters. Hopefully I will finally remember this non-intuitive set of functions now that I shared it.

This is a 66th post of #100daystooffload.