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From: "Matthew Heaney" <matthew_heaney@acm.org>
Subject: Re: Safely converting String to Float ?
Date: 1999/11/03
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References: <m3n1svbw6t.fsf@kiuk0156.chembio.ntnu.no>
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In article <m3n1svbw6t.fsf@kiuk0156.chembio.ntnu.no> , Preben Randhol 
<randhol@pvv.org>  wrote:

> begin
>    Get(Tekst,Tall,Size);
>    Get(Tekst2,Tall_F,Size_F);
> end;

Use an exception handler:

  begin
    Get (Tekst, Tall, Size);
  exception
    when Data_Error =>         -- check this in the RM
      Put_Line (<whatever>);
  end;

  begin
    Get (...);
  exception
    when Data_Error =>
     Put_Line (...);
  end;


A few more points:

1) If you're using type Float, you don't need to instantiate
Text_IO.Float_IO, because there's a predefined package called
Ada.Float_Text_IO.


2) If you use Get, then the last parameter is not a "size" of subtype
"Integer," it indicates the last index position of the value image, and
its subtype is "Natural."

  declare
    Image : String := "<image of floating point value>";
    Value : Float;
    Last  : Positive;
  begin
    Get (From => Image, Item => Value, Last => Last);
  exception
    when Data_Error =>
      <handle error>
  end;


3) You don't really need Float_Text_IO or Get; simply use the attribute
Float'Value to convert the string:

  declare
    Image : String := <whatever>;
    Value : Float;
  begin
    Value := Float'Value (Image);
  exception
    when Constraint_Error =>      -- note different exception
      <handle error>
  end;





--
Evolution is as well documented as any phenomenon in science, as
strongly as the earth's revolution around the sun rather than vice
versa.

Stephen Jay Gould, Time, 23 Aug 1999