Ada Conformity Assessment Authority      Home Conformity Assessment   Test Suite ARGAda Standard
Ada Reference ManualLegal Information
Contents   Index   References   Search   Previous   Next 

11.4 Exception Handling

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

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. 
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: 
If the construct is a task_body, the exception does not propagate further; 
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;
Otherwise, the occurrence is propagated to the innermost dynamically enclosing execution, which means that the occurrence is raised again in that context. 
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.
2  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. 

Contents   Index   References   Search   Previous   Next 
Ada-Europe Ada 2005 and 2012 Editions sponsored in part by Ada-Europe