[Info-vax] String handling, was: Re: C... the only winning move is not to play...

[Simon Clubley]

On 2014-02-14, David Froble <davef at tsoft-inc.com> wrote:
>
> Basic supports various types of strings, dynamic, fixed length, 
> constants, MAPs, and so forth.
>
> Yes, if you declare a static string, that's there, nothing more to do 
> except move data in and out.
>
> A dynamic string, every time it's set, must determine whether the 
> current storage can be used, and if not, (I'm guessing a bit here), 
> deallocate the current storage and allocate new storage of the desired 
> length.  I heard once that if the new string is smaller, it uses the 
> same storage, but, I'm not sure then how it knows that the storage is 
> longer than the current string.
>

For comparison, Ada has a half-way datatype, between fixed length and
fully dynamic strings, called Bounded_String in which space up to a
maximum length is pre-allocated but it's otherwise treated as a
dynamic string.

It's more efficient than a fully dynamic string, but at the expense of
allocating the memory for the maximum string size up front.

The Bounded_String package specification is here:

https://www2.adacore.com/gap-static/GNAT_Book/html/aarm/AA-A-4-4.html

and a readable example comparing the three basic string handling options
in Ada is here:

http://en.wikibooks.org/wiki/Ada_Programming/Strings

>
> I will observe that it would be rare to have string manipulation in a 
> loop that executes thousands (or more) times.  But it can happen.

Have you ever written a parser ? :-)

Simon.

-- 
Simon Clubley, clubley at remove_me.eisner.decus.org-Earth.UFP
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