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11.2 Exception Handlers
1
The response to one or more exceptions is specified
by an exception_handler.
Syntax
2
handled_sequence_of_statements
::=
sequence_of_statements
[
exception
exception_handler
{
exception_handler}]
3
exception_handler
::=
when [
choice_parameter_specification:]
exception_choice {|
exception_choice} =>
sequence_of_statements
4
choice_parameter_specification
::= defining_identifier
5
exception_choice
::= exception_name |
others
Legality Rules
6
A choice with an
exception_name
covers the named exception. A choice with
others covers
all exceptions not named by previous choices of the same
handled_sequence_of_statements.
Two choices in different
exception_handlers
of the same
handled_sequence_of_statements
shall not cover the same exception.
7
A choice with others is allowed only for
the last handler of a handled_sequence_of_statements
and as the only choice of that handler.
8
An exception_name
of a choice shall not denote an exception declared in a generic formal
package.
Static Semantics
9
A
choice_parameter_specification
declares a
choice parameter, which is a constant object of type
Exception_Occurrence (see
11.4.1). During
the handling of an exception occurrence, the choice parameter, if any,
of the handler represents the exception occurrence that is being handled.
Dynamic Semantics
10
The execution of a
handled_sequence_of_statements
consists of the execution of the
sequence_of_statements.
The optional handlers are used to handle any exceptions that are propagated
by the
sequence_of_statements.
Examples
11
Example of an
exception handler:
12
begin
Open(File, In_File, "input.txt"); -- see A.8.2
exception
when E : Name_Error =>
Put("Cannot open input file : ");
Put_Line(Exception_Message(E)); -- see 11.4.1
raise;
end;
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