Re: Strings and reading from a file

[Marin David Condic <condicma@bogon.pwfl.com>]

Cameron Hodge wrote:
> 
> True enough. I was just hoping not to have to create another array.
> 
You may be missing the point. Look at the packages in appendix A.4 of
the ARM. Specifically, I'd recommend Ada.Strings.Unbounded in A.4.5. You
have a type called Unbounded_String. You also have a function: "Length"
that operates on Unbounded_String. Also functions To_Unbounded_String
and To_String will be useful to you here. If you have an array of
Unbounded_String, you can store whatever strings you read in and their
lengths will be remembered.

As you're reading in strings, you get the length as one of the returned
parameters. You can "slice" the string to be just that length - thus
removing anything that is garbage. The trick is to write yourself a
function that returns a value of type String. Internally, it declares
some sufficiently large String variable to handle a worst case, but it
only returns the slice. (The space is recovered off the stack when the
function returns, so it isn't wasted.) Do something like:

function Next_Line return String is
    Str  : String (1..256) ;
    Len  : Natural ;
begin
    Get_Line (
        Item  => Str,
        Last  => Len) ;
    return Str (1..Len) ;
end Next_Line ;

You can dress up the function to make it look as pretty as you like -
maybe even make it a general-purpose utility by adding a file parameter,
etc. Somewhere between this and the features you have in
Ada.Strings.Unbounded you can do whatever you like with flexible sized
strings and you won't have to fuss with leftover garbage, unused space
or anything else inconvenient. Of course, the price you pay for the
convenience may be some additional execution speed or memory
utilization, but unless you are working on something with a real time
sensitivity, this should not be much of a concern.

MDC
-- 
Marin David Condic
Real Time & Embedded Systems, Propulsion Systems Analysis
United Technologies, Pratt & Whitney, Large Military Engines
M/S 731-95, P.O.B. 109600, West Palm Beach, FL, 33410-9600
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