Re: I am not understanding user defined exceptions

[Dennis Lee Bieber <wlfraed@ix.netcom.com>]

On Fri, 3 Feb 2017 12:27:09 -0800 (PST), patrick@spellingbeewinnars.org
declaimed the following:

>
>If we type something like :    
>         if x = 1
>         then
>           raise Foo_Error;
>         end if ;
> 
>will x not be tested for exceptions conditions automatically from that point onward? If so, why would it not raise an exception if the second text_io.get came back with 1 ?
>

	No... because that is just a sequence of statements that only take
effect /at that location/. Ada doesn't magically go back and apply that
code whenever you do something with the variable X.

	If you always need to have input of a 1 raise the exception, you need
to encapsulate the input with the test. See below:

-=-=-=-=-=-
with Ada.Integer_Text_Io;
with Ada.Text_IO;

procedure Test_Exceptions is
   
   Foo_Error : exception;
   
   X : Integer;
   
   procedure Get_Int (An_Int : out Integer) is
   begin
      Ada.Text_IO.Put ("Enter an integer => ");
      
      Ada.Integer_Text_IO.Get (An_Int);
      
      if An_Int = 1 then
	 raise Foo_Error;
      end if;
   end Get_Int;
   
begin
   Get_Int (X);   -- first input point
   Get_Int (X);    -- second input point
   
   Ada.Text_Io.Put_Line ("Ended without exceptions...");
      
exception
   when Foo_Error =>
      Ada.Text_Io.Put_Line ("Error handled...");
      
end Test_Exceptions;

-=-=-=-=-=-

C:\Users\Wulfraed\Ada>test_exceptions
Enter an integer => 1
Error handled...

C:\Users\Wulfraed\Ada>test_exceptions
Enter an integer => 2
Enter an integer => 1
Error handled...

C:\Users\Wulfraed\Ada>test_exceptions
Enter an integer => 3
Enter an integer => 2
Ended without exceptions...
-- 
	Wulfraed                 Dennis Lee Bieber         AF6VN
    wlfraed@ix.netcom.com    HTTP://wlfraed.home.netcom.com/