[Info-vax] String handling

[Stephen Hoffman]

On 2014-02-15 16:51:21 +0000, Simon Clubley said:

> I was asking about VMS Basic (ie: DEC/CPQ/HP Basic) not about how VMS 
> implements string handling.
> 
> IOW, when David talked about fixed strings in VMS Basic, did he really 
> mean fixed strings in the sense of Ada's String data type in which the 
> length is immutable, or did he really mean something closer to Ada's 
> Bounded_String data type ?

The DEC BASIC fixed-length strings use scaler-class string descriptors, 
and the string contents are exact-fit / force-fit.  The text strings 
are truncated or are space-padded to fit, as required.

Based on <http://en.wikibooks.org/wiki/Ada_Programming/Strings>, what 
BASIC does with fixed-length strings is slightly simpler than what Ada 
provides with its bound strings.  Ada has two string length values 
around; the current string length and the (potentially implicit) 
maximum string length.  With BASIC, you have one length.  To achieve 
what Ada offers here, you'd have to calculate the length at run-time 
and maintain it in parallel to the string, if you wanted or needed the 
Ada bounded string behavior.

Were this C, Macro32, Bliss or analogous, somebody would suggest just 
adjusting the embedded descriptor length directly.

Programming environments that provide garbage collection can change 
your view on storage allocation and management, too.

As with anything in computing, there are performance and memory 
trade-offs lurking here, whether with it's scalar / static strings, 
dynamic strings, or garbage-collected environments.


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