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From: Jeff Shipman <shippy@nmt.edu>
Newsgroups: comp.lang.ada
Subject: newbie can't get exceptions to work!
Date: Wed, 04 Apr 2001 21:19:18 -0600
Organization: New Mexico Institute of Mining and Technology
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Date: 2001-04-04T21:19:18-06:00
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Ok, I'm creating a generic stack package and I think
I've done everything properly, but I cannot seem to
get my STACK_EXCEPTION to work. This is what it
looks like in my gen_stack.ads file:

generic
   LEN : NATURAL := 100;      -- Size of the stack (default 100
   type ELM is private;       -- Used to store element type

   package GEN_STACK is
      STACK_ERROR : exception;        -- Raised when something bad
happens.
      
      procedure PUSH(E : in ELM);     -- Push E into the stack
      procedure POP(E : out ELM);     -- Pop element from stack; store
in E
      
      function  FULL return BOOLEAN;  -- Returns TRUE if stack is full
      function  EMPTY return BOOLEAN; -- Returns TRUE if stack is empty
   end GEN_STACK;

and I can use it just fine in my gen_stack.adb. The use_gen_stack.adb
file which uses the stacks works great up until the point I want to
handle the exceptions. My code for handling it looks like this:

   -- Handle exceptions
   exception
      when STACK_ERROR =>
      begin
         put_line("Error: Stack underflow/overflow");
      end;

When I try to compile, I get the following errors:

use_gen_stack.adb:214:12: "STACK_ERROR" is not visible
use_gen_stack.adb:214:12: multiple use clauses cause hiding
use_gen_stack.adb:214:12: hidden declaration at gen_stack.ads:14,
instance at line 32
use_gen_stack.adb:214:12: hidden declaration at gen_stack.ads:14,
instance at line 31
use_gen_stack.adb:214:12: hidden declaration at gen_stack.ads:14,
instance at line 30
use_gen_stack.adb:214:12: hidden declaration at gen_stack.ads:14,
instance at line 29
use_gen_stack.adb:214:12: hidden declaration at gen_stack.ads:14,
instance at line 28
use_gen_stack.adb:214:12: hidden declaration at gen_stack.ads:14,
instance at line 27
gnatmake: "use_gen_stack.adb" compilation error
make: *** [use_gen_stack] Error 4

Those relevant lines of code are:

   -- Convenient stack types we'll need
   package INT_STACK is new GEN_STACK(ELM => INTEGER, LEN => 10);
   package INT2_STACK is new GEN_STACK(ELM => INTEGER, LEN => 5);
   package FLOAT_STACK is new GEN_STACK(ELM => FLOAT, LEN => 12);
   package CHAR_STACK is new GEN_STACK(ELM => CHARACTER, LEN => 14);
   package STR_STACK is new GEN_STACK(ELM => STR, LEN => 3);
   package DAY_STACK is new GEN_STACK(ELM => DAY, LEN => 7);

   use INT_STACK; use INT2_STACK; use FLOAT_STACK;
   use CHAR_STACK; use STR_STACK; use DAY_STACK;

At the top of my file, I have the following:

with text_io; use text_io;
with ada.float_text_io; use ada.float_text_io;
with gen_stack;

I've tried putting in use STACK_ERROR in multiple
places. I just can't get this exception handler
to compile. I would greatly appreciate it if someone
could help me. I'm sure it's a very simple thing
I'm forgetting. By the error message, it seems like
it doesn't like the multiple instances of use, but
If I want to use those packages I created, I have
to do that!

Thanks in advance,
 
Jeff "Shippy" Shipman     E-Mail: shippy@nmt.edu
Computer Science Major    ICQ: 1786493
New Mexico Institute of Mining and Technology
Homepage: http://www.nmt.edu/~shippy