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11.4 Exception Handling
1
When an exception occurrence is raised, normal
program execution is abandoned and control is transferred to an applicable
exception_handler, if any.
To
handle an exception occurrence is to respond to the exceptional
event.
To
propagate an exception occurrence
is to raise it again in another context; that is, to fail to respond
to the exceptional event in the present context.
Dynamic Semantics
2
Within
a given task, if the execution of construct
a is defined by this
International Standard to consist (in part) of the execution of construct
b, then while
b is executing, the execution of
a
is said to
dynamically enclose the execution of
b.
The
innermost dynamically enclosing execution of a given execution
is the dynamically enclosing execution that started most recently.
3
When
an exception occurrence is raised by the execution of a given construct,
the rest of the execution of that construct is
abandoned; that
is, any portions of the execution that have not yet taken place are not
performed. The construct is first completed, and then left, as explained
in
7.6.1. Then:
4
- If the construct is a task_body,
the exception does not propagate further;
5
- If the construct is the sequence_of_statements
of a handled_sequence_of_statements
that has a handler with a choice covering the exception, the occurrence
is handled by that handler;
6
- Otherwise, the
occurrence is propagated to the innermost dynamically enclosing
execution, which means that the occurrence is raised again in that context.
7
When
an occurrence is
handled by a given handler, the
choice_parameter_specification,
if any, is first elaborated, which creates the choice parameter and initializes
it to the occurrence. Then, the
sequence_of_statements
of the handler is executed; this execution replaces the abandoned portion
of the execution of the
sequence_of_statements.
8
1 Note that exceptions
raised in a declarative_part of
a body are not handled by the handlers of the handled_sequence_of_statements
of that body.
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