Re: Concatenation and Characters

[Georg Bauhaus <sb463ba@l1-hrz.uni-duisburg.de>]

Justin Birtwell <jbirtwell@yahoo.com> wrote:
:  How can you declare a string variable when
: you don't know before hand what the string is going to be? 

If you don't known the length, you can't.
However, it depends on the extent of "beforehand".
Say you arrive at some point in your program where you want to
store some text in a string, to be used locally. Then you will
have a means (function) to find its length because you know what
is going to be stored in the string and
declare
   calculated_length: constant natural := image_length_of (some_data);
   booklet: constant string(1..calculated_length) := image_of (some_data);
begin
  --- use booklet
end;

Otherwise you need either bounded strings or unbounded strings,
and you will need the operations for them, to store information
the way you indicated. The operations are provided by Ada.Strings.*
packages, which see, or perhaps some chapter about strings? It's
good reading anyway, as (apparently) years of experience in string
handling have influenced the design of these packages, and so they
are full of useful information.

Sometimes it might also be more useful to just not store the information
in string variables and instead pass it on to where it is used, via
subprogram parameters.

-- Georg