Elisp / How to insert a char at a fixed position in a string
reddit / emacs

----------------------------------------------------------------------
konrad1977 · 2022-09-08 16:16

Let say you have

    (setq myId "00223344556677")

and now you want to format it as "002233-44556677"

I can't find a good way to insert a character.

Thanks

----------------------------------------------------------------------
MitchellMarquez42 · 2022-09-08 16:31

I'd use a temp buffer `(with-temp-buffer)`.

Insert the value of myId

`(goto-char) ` wherever you want to put the hyphen

Insert it

Get the text from the buffer, for example with `(buffer-substring-no-
properties)`

----------------------------------------------------------------------
raevnos · 2022-09-08 17:09

(concat (substring myId 0 6) "-" (substring myId 6))

----------------------------------------------------------------------
konrad1977 · 2022-09-08 17:19

Thanks, exactly what I was looking for.

----------------------------------------------------------------------
c256 · 2022-09-10 04:38

Are you doing this enough to worry about efficiency? If so, you might
care that string literals are effectively immutable in elisp (IIRC),
and so taking a string apart and adding pieces will create multiple
strings in memory. Garbage Collection means that you don’t have to
worry about memory management, until you’re doing something
often/quickly enough that gc becomes a concern.
(The alternative is *probably* to use **and re-use** an emacs buffer,
which is expressly designed to hold mutable sequences of characters.)

----------------------------------------------------------------------
konrad1977 · 2022-09-10 05:29

One timer, just to fix the correct id to send to the compiler. So no.
But thanks for the heads up!