Re: A simple ADA puzzle (I haven't the answer)

[Brian May <bam@snoopy.apana.org.au>]

>>>>> "Frank" == Frank J Lhota <NOSPAM.lhota.adarose@verizon.net> writes:

    Frank> The answer depends heavily on how Unbounded_String is
    Frank> implemented, and that will vary from compiler to
    Frank> compiler. However, I think I know what point you're getting
    Frank> at: the Unbounded_String solution has its own storage
    Frank> overhead, and that if the strings involved are all short
    Frank> enough, the Unbounded_String approach may actually use more
    Frank> memory.

This is an issue where there is a tradeoff between efficiency of the
program and how general it can be.

(note: when I say "you" read as "the programmer or the
interpreter/compiler").

If you want fixed length strings, then you are stuck with a fixed
length, but you get maximum use of memory, and minimal overheads.

If you want variable length strings, but have a maximum length, you
can allocate up to this maximum length, but you need to keep track of
the actual length used somehow, eg. by counting bytes or adding a null
terminator at the end of the string. Also if you accidently exceed
this length, you will get undesired results (unless you are using Ada
and can somehow gracefully deal with the exception).

If you want variable length strings, with no maximum limit, then you
need to allocate/free memory dynamically at run time and keep track of
the length allocated.

Some languages may try to hide these issues (to various degrees) from
the programmers, but they still remain issues which may be important
with some applications (eg. time critical applications).

At least Ada not only allows you to choose which one you want (like C
or C++), but it will also enforce your choice to, so you can't exceed
the maximum length for instance and allow corrupting surrounding data.

Similar issues also arise with arrays.
-- 
Brian May <bam@snoopy.apana.org.au>