Re: substr() - copying or not copying, that is here the question.

On 2025-05-31, Mack The Knife <mack@the-knife.org> wrote:

In article <101f9oo$18edp$1@dont-email.me>,
Janis Papanagnou  <janis_papanagnou+ng@hotmail.com> wrote:

In the context   p=index(substr(t,s),r)
it would not be necessary to copy the substr(t,s),
the index() function could operate on the original
using some access "descriptor" (say, a pointer and
a length) in read-only mode.
>
Will (GNU) Awk do a copy of the data value or does
it use a read-only descriptor access to the already
existing substring of variable "t"?
>
Currently I'm playing with some huge data and copies
of MB sized data is costly (if it's repeatedly done
with various substr() subscripts).

>
substr() makes a copy. This is clear in the code.
>
It's almost impossible to do this via read-only descriptor.

It's entirely possible, with just reference counted memory management.
Under the hood, you have two kinds of string types: primary strings, and
strings which are views displaced into other strings. The displacing
strings own a reference count on the target string, and indicate the
offset and range.

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