Ada Programming/Libraries/Ada.Exceptions

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This language feature is available from Ada 95 on.

Ada.Exceptions is a unit of the Predefined Language Environment since Ada 95.

The package Ada.Exceptions allows you to analyze exceptions you have caught, to raise exceptions with an associated message or to save exceptions occurrences for later processing.

Usage

The following example shows how to implement a "last resort" error handler which just displays the information related to the error which occurred.

File: numeric_6.adb (view, plain text, download page, browse all)

with Ada.Exceptions;

procedure Numeric_6 is
  package Exept renames Ada.Exceptions;
...
           exception
              when An_Exception : others =>
                 T_IO.Put_Line
                   (Exept.Exception_Information (An_Exception));
           end Try;

Specification

--                     Standard Ada library specification
--   Copyright (c) 2003-2018 Maxim Reznik <reznikmm@gmail.com>
--   Copyright (c) 2004-2016 AXE Consultants
--   Copyright (c) 2004, 2005, 2006 Ada-Europe
--   Copyright (c) 2000 The MITRE Corporation, Inc.
--   Copyright (c) 1992, 1993, 1994, 1995 Intermetrics, Inc.
--   SPDX-License-Identifier: BSD-3-Clause and LicenseRef-AdaReferenceManual
-- -------------------------------------------------------------------------

with Ada.Streams;

package Ada.Exceptions is

   pragma Preelaborate (Exceptions);

   type Exception_Id is private;
   pragma Preelaborable_Initialization (Exception_Id);

   Null_Id : constant Exception_Id;

   function Exception_Name (Id : in Exception_Id) return String;

   function Wide_Exception_Name (Id : in Exception_Id) return Wide_String;

   function Wide_Wide_Exception_Name (Id : in Exception_Id)
     return Wide_Wide_String;

   type Exception_Occurrence is limited private;
   pragma Preelaborable_Initialization (Exception_Occurrence);

   type Exception_Occurrence_Access is access all Exception_Occurrence;

   Null_Occurrence : constant Exception_Occurrence;

   procedure Raise_Exception (E       : in Exception_Id;
                              Message : in String := "");
   pragma No_Return (Raise_Exception);

   function Exception_Message (X : in Exception_Occurrence) return String;

   procedure Reraise_Occurrence (X : in Exception_Occurrence);

   function Exception_Identity (X : in Exception_Occurrence)
     return Exception_Id;

   function Exception_Name (X : in Exception_Occurrence) return String;
   --   Same as Exception_Name(Exception_Identity(X)).

   function Wide_Exception_Name (X : in Exception_Occurrence)
     return Wide_String;
   --   Same as Wide_Exception_Name(Exception_Identity(X)).

   function Wide_Wide_Exception_Name (X : in Exception_Occurrence)
     return Wide_Wide_String;
   --   Same as Wide_Wide_Exception_Name(Exception_Identity(X)).

   function Exception_Information (X : in Exception_Occurrence) return String;

   procedure Save_Occurrence (Target :    out Exception_Occurrence;
                              Source : in     Exception_Occurrence);

   function Save_Occurrence (Source : in Exception_Occurrence)
     return Exception_Occurrence_Access;

   procedure Read_Exception_Occurrence
    (Stream : not null access Ada.Streams.Root_Stream_Type'Class;
     Item   : out Exception_Occurrence);

   procedure Write_Exception_Occurrence
    (Stream : not null access Ada.Streams.Root_Stream_Type'Class;
     Item   : in Exception_Occurrence);

   for Exception_Occurrence'Read use Read_Exception_Occurrence;
   for Exception_Occurrence'Write use Write_Exception_Occurrence;

private

   pragma Import (Ada, Exception_Id);
   pragma Import (Ada, Exception_Occurrence);
   pragma Import (Ada, Null_Id);
   pragma Import (Ada, Null_Occurrence);

end Ada.Exceptions;

See also

Wikibook

• Ada Programming/Libraries/Ada
• Ada Programming/Strings

External examples

• Search for examples of Ada.Exceptions in: Rosetta Code, GitHub (gists), any Alire crate or this Wikibook.
• Search for posts related to Ada.Exceptions in: Stack Overflow, comp.lang.ada or any Ada related page.

Ada Reference Manual

Ada 95

• 11.4.1: The Package Exceptions ^[Annotated]

Ada 2005

• 11.4.1: The Package Exceptions ^[Annotated]

Ada 2012

• 11.4.1: The Package Exceptions ^[Annotated]

Open-Source Implementations

FSF GNAT

• Specification: a-except.ads
• Body: a-except.adb

drake

• Specification: a-except.ads
• Body: a-except.adb