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11.2 Exception Handlers

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The response to one or more exceptions is specified by an exception_handler.

Syntax

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handled_sequence_of_statements::=
     sequence_of_statements
  [exception
     exception_handler
    {exception_handler}]

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exception_handler::=
  when [choice_parameter_specification:] exception_choice {| exception_choice} =>
     sequence_of_statements

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choice_parameter_specification::= defining_identifier

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exception_choice::= exception_name others
Legality Rules

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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 (see 11.2). Two choices in different exception_handlers of the same handled_sequence_of_statements (see 11.2) shall not cover the same exception.

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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.

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An exception_name of a choice shall not denote an exception declared in a generic formal package.

Static Semantics

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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

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The execution of a handled_sequence_of_statements consists of the execution of the sequence_of_statements (see 5.1). The optional handlers are used to handle any exceptions that are propagated by the sequence_of_statements (see 5.1).

Examples

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Example of an exception handler:

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     begin
        Open(File, In_File, "input.txt");   −− see A.8.2
     exception
        when Name_Error =>
           Put("Cannot open input file ");
           Put_Line(Exception_Message(E));  −− see 11.4.1
           raise;
     end;