How do I return a particular character from a text?

Question

How do I return a particular character from a text? For example:

text = "Eu sou vegano"

How do I detect the 5th letter of text? If anyone would help me, I’d be grateful.

Answer 1

You can use the command string.sub:

> string.sub(text, 5, 5)
o

This command takes as parameters the string, the initial position and the final position.

If the final position is not reported, it assumes the final position of the string. Example:

> string.sub(text, 5)
ou vegano

Answer 2

The reply of @Gomiero is super correct. Additionally, I recommend using a library to manipulate strings that use byte-based encodings.

This is not complicated, and is essential since usually only 256 character types can be represented in the Lua string type, that is, the strings contain a string of bytes, not characters. These bytes are considered character codes.

Several renderers render texts based on UTF-8 text encoding. Some programming languages implement UTF-16 natively, but Lua would not be one of these.

As UTF-8 or ASCII (I think, ASCII...) are common, it is possible for a code in Lua to obtain characters encoded automatically through text boxes, snippets, and mainly files.

So, yes... that’s it. A string contains a collection of Lua bytes.

When my laptop is fixed, maybe I’ll try to improve my answer.

UTF-8

Version 5.3 of Lua already offers a library (utf8) to work with UTF-8 strings, including a syntax of \u{código} almost similar to Ecmascript, only encoding a character in UTF-8, and only usable in strings where it is special.

The library only has a sub-type function, but you can make a copy using its methods:

do
    local offset, sub = utf8.offset, string.sub;

    function utf8:sub(i, j)
        i, j = tonumber(i) or 1,
               tonumber(j) or -1;

        local len = utf8.len(self);

        i, j = ( i < 0 ) and ( ( len + 1 ) + i ) or i,
            ( j < 0 ) and ( ( len + 1 ) + j ) or j;

        i, j = ( i < 1 ) and 1 or i,
            ( j > len ) and len or j;

        if ( j < i ) then
            return '';
        end

        i, j = offset(self, i),
            offset(self, j + 1);

        return sub(self, i, j - 1);
    end

end

Then the use goes like this:

print(
    utf8.sub('wowow䀀3', 6, 6) --> 䀀
);

Love2d also supports the same library (documentation), but I don’t know if the Lua version is equivalent.

And there’s a project on Github that offers a similar library, with few differences (Stepets/utf8.moon) and already offers a sub function.

UTF-16

One day I tried to make a library to manipulate UTF-16. It was made anyway just to see if it worked. Besides, it’s incomplete, but when my laptop gets fixed, maybe I’ll recreate it: utf16.

So far I don’t know any other encodings..