Contents Index Search Previous Next
11.4.1 The Package Exceptions
The following language-defined
library package exists:
package Ada.Exceptions is
type Exception_Id is private;
Null_Id : constant Exception_Id;
function Exception_Name(Id : Exception_Id) return String;
type Exception_Occurrence is limited private;
type Exception_Occurrence_Access is access all Exception_Occurrence;
Null_Occurrence : constant Exception_Occurrence;
procedure Raise_Exception(E : in Exception_Id;
Message : in String := "");
function Exception_Message(X : Exception_Occurrence) return String;
procedure Reraise_Occurrence(X : in Exception_Occurrence);
function Exception_Identity(X : Exception_Occurrence)
function Exception_Name(X : Exception_Occurrence) return String;
-- Same as Exception_Name(Exception_Identity(X)).
function Exception_Information(X : Exception_Occurrence) return String;
procedure Save_Occurrence(Target : out Exception_Occurrence;
Source : in Exception_Occurrence);
function Save_Occurrence(Source : Exception_Occurrence)
... -- not specified by the language
Each distinct exception is represented by a distinct
value of type Exception_Id. Null_Id does not represent any exception,
and is the default initial value of type Exception_Id. Each occurrence
of an exception is represented by a value of type Exception_Occurrence.
Null_Occurrence does not represent any exception occurrence, and is the
default initial value of type Exception_Occurrence.
For a prefix
E that denotes an exception, the following attribute is defined:
E'Identity returns the unique
identity of the exception. The type of this attribute is Exception_Id.
Raise_Exception raises a new occurrence of the
identified exception. In this case, Exception_Message returns the Message
parameter of Raise_Exception. For a raise_statement
with an exception_name, Exception_Message
returns implementation-defined information about the exception occurrence.
Reraise_Occurrence reraises the specified exception occurrence.
Exception_Identity returns the identity of the
exception of the occurrence.
The Exception_Name functions return the full
expanded name of the exception, in upper case, starting with a root library
unit. For an exception declared immediately within package Standard,
the defining_identifier is returned.
The result is implementation defined if the exception is declared within
an unnamed block_statement.
Exception_Information returns implementation-defined
information about the exception occurrence.
Raise_Exception and Reraise_Occurrence have no
effect in the case of Null_Id or Null_Occurrence.
Exception_Identity, Exception_Name, and Exception_Information raise Constraint_Error
for a Null_Id or Null_Occurrence.
The Save_Occurrence procedure copies the Source
to the Target. The Save_Occurrence function uses an allocator
of type Exception_Occurrence_Access to create a new object, copies the
Source to this new object, and returns an access value designating this
new object; the result may be deallocated using an instance of Unchecked_Deallocation.
The implementation of the Write attribute (see
) of Exception_Occurrence shall
support writing a representation of an exception occurrence to a stream;
the implementation of the Read attribute of Exception_Occurrence shall
support reconstructing an exception occurrence from a stream (including
one written in a different partition).
An implementation of Exception_Name in a space-constrained
environment may return the defining_identifier
instead of the full expanded name.
The string returned by Exception_Message may
be truncated (to no less than 200 characters) by the Save_Occurrence
procedure (not the function), the Reraise_Occurrence procedure, and the
Exception_Message (by default) and Exception_Information
should produce information useful for debugging. Exception_Message should
be short (about one line), whereas Exception_Information can be long.
Exception_Message should not include the Exception_Name. Exception_Information
should include both the Exception_Name and the Exception_Message.
Contents Index Search Previous Next Legal