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

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Janis Papanagnou <janis_papanagnou+ng@hotmail.com> writes:

> On 31.05.2025 21:07, Mack The Knife 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.
>
> Okay. Thanks for checking that!
...
> Okay, maybe I could write an extension to work on memory
> mapped files - the data originally stems from a file -
> and seek/read through "C" mechanisms. (But that's huge
> effort compared to some natively available function. And
> then I'd probably better implement that straightly in "C"
> instead of using Awk, in the first place, since I'd have
> to implement the GNU Awk Extension anyway in "C".)

An alternative (depending on the context) would be to consider an
extension that provides an index function with a third argument giving
the initial offset.  I've not looked at how extensions get access to
GAWK strings, so this many not be as easy as it sounds, but I would
guess that it might be relatively simple to do.

-- 
Ben.

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Thread

substr() - copying or not copying, that is here the question. Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-05-31 18:12 +0200
  Re: substr() - copying or not copying, that is here the question. mack@the-knife.org (Mack The Knife) - 2025-05-31 19:07 +0000
    Re: substr() - copying or not copying, that is here the question. Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-06-01 00:16 +0200
      Re: substr() - copying or not copying, that is here the question. Ben Bacarisse <ben@bsb.me.uk> - 2025-06-01 11:42 +0100
        Re: substr() - copying or not copying, that is here the question. Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-06-01 13:43 +0200
          Re: substr() - copying or not copying, that is here the question. gazelle@shell.xmission.com (Kenny McCormack) - 2025-06-01 12:06 +0000
            Re: substr() - copying or not copying, that is here the question. Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-06-01 15:27 +0200
        Re: substr() - copying or not copying, that is here the question. gazelle@shell.xmission.com (Kenny McCormack) - 2025-06-01 11:53 +0000
          Re: substr() - copying or not copying, that is here the question. Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-06-01 15:47 +0200
            Re: substr() - copying or not copying, that is here the question. gazelle@shell.xmission.com (Kenny McCormack) - 2025-06-01 14:17 +0000
              Re: substr() - copying or not copying, that is here the question. Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-06-08 00:01 +0200
      Re: substr() - copying or not copying, that is here the question. mack@the-knife.org (Mack The Knife) - 2025-06-03 06:56 +0000
        Re: substr() - copying or not copying, that is here the question. gazelle@shell.xmission.com (Kenny McCormack) - 2025-06-03 11:04 +0000
        Re: substr() - copying or not copying, that is here the question. Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-06-08 00:05 +0200
          Re: substr() - copying or not copying, that is here the question. mack@the-knife.org (Mack The Knife) - 2025-06-08 12:35 +0000
            Re: substr() - copying or not copying, that is here the question. Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-06-11 11:07 +0200
              Meta chat (Was: substr() - copying or not copying, that is here the question.) gazelle@shell.xmission.com (Kenny McCormack) - 2025-06-11 12:11 +0000
    Re: substr() - copying or not copying, that is here the question. Kaz Kylheku <643-408-1753@kylheku.com> - 2025-06-01 00:01 +0000

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