String Manipulation: Why Isn't string.sub Working Correctly? [RE-POST, THREAD DELETED] [closed]
A thread was recently made about string.sub working incorrectly, but the question was deleted before I could answer. The problem was an easy one to make; the code looked similar to:
1 | local s = "Hello world!" |
2 | print(s:sub(1, 5) == "ell") --> false -- why? |
I'll post my answer to this question below for those who may come across a similar issue.
2 answers
Your issue is in inclusiveness. The full syntax of string.sub is:
s:sub(int i, int j)/string.sub(string s, int i, [int] j)
Return the substring of s that starts at i and ends at j; i and j can be negative. If j is absent, then it is assumed to be equal to -1 (which is the same as the string length).
i and j are inclusive; they are included in the substring:
1 | local s = "Hello world!" |
2 | print(s:sub(2, 4)) --> ell -- e is the 2nd character, l is the 4th character. |
In your script, you do not account for this inclusion, which is why you are receiving unexpected results.
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You are assuming that the index of the substring begins at 0, which in fact in Lua, begins at 1!
1 | local s = "Hello world!" |
2 |
3 | print(s:sub(1, 5)); |
would print Hello. Not ello which is what you are assuming right now. Many other languages's index begins at 0 which is why you are confusing yourself right now.
To fix your problem, simply start from 2.
1 | local s = "Hello world!" |
2 |
3 | print(s:sub(2, 5) == "ello"); |
which would evaluate to true.
That is the real issue here. There really is nothing wrong with the syntax itself. It is simply a Logical Error.
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Closed as off-topic by Zafirua and yHasteeD
This question has been closed by our community as being off-topic from ROBLOX Lua Scripting.
Why was this question closed?