Experimental Physics and
Industrial Control System

Benjamin Franksen <[email protected]> · Wed, 20 Jul 2005 21:21:28 +0200

On Wednesday 20 July 2005 18:11, Andrew Johnson wrote:
> Kay-Uwe Kasemir wrote:
> > How would you prefer to handle these?
> > a) equip the EpicsString class with all the methods
> >    to change/insert/delete character sequences at any
> >    position in the string
> > b) have a
> >       char buf[...]
> >    where you can to all the character fiddling,
> >    then attach a string interface to that in order
> >    to hand it to the CA Server or other EPICS entity?
> >    So this String class would actually be non-mutable,
> >    it only provides read-access to the user-owned buf.
> >
> > I would prefer b, so we have another example for
> > my case that the most important task of the string class
> > it to interface with char *.
>
> c) Design the string class so that it has an internal API giving
> access to the raw data buffer.  Provide a set of manipulator
> functions that use this API to perform the string operations that we
> need.  Permit anyone else to write additional manipulators for
> operations they need which we haven't implemented.

d) Variant of b): Have a separate class for constructing a string. It 
should maintain a current char[] buffer, so that characters can be 
efficiently appended, but is extensible in size and supports operations 
like DA's streamWrite (with write position at the end only).

On Wednesday 20 July 2005 17:12, Andrew Johnson wrote:
> There is a record type called the stringCalc record, which is used
> extensively by the BCDA group's synApps software (among other things,
> it permits you to interface to new ASCII devices without having to
> write device support).  The VAL field of a stringCalc is string,
> which is regenerated every time the record processes.  I don't know
  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> how you would implement this record type if all strings become
> read-only once created.

You already answered your question: The string gets regenerated every 
time. It's a new string, different from the old one. No destructive 
update of the string is necessary to achieve that.

Ben

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System