CODEWITHSUNDEEP
ada
jacob
jacob

Reputation: 4956

Catch Precondition Assert_Failure

I'm trying to catch the error in this precondition I have on the main procedure and I'm wondering if it's possible to catch? Do I need to move this to a different procedure and then call it in main in order to catch it?

 with
    ada.text_io,
    ada.command_line,
    ada.strings.bounded,
    system.assertions;

 procedure main with
    pre => (ada.command_line.argument_count > 2)
 is
    package b_str is new
        ada.strings.bounded.generic_bounded_length (max => 255);
    use b_str;

    input_file : bounded_string;
    argument : bounded_string;
    i : integer := 1;
 begin
    while i <= ada.command_line.argument_count loop
        argument := to_bounded_string(
            ada.command_line.argument(i)
        );

         ada.text_io.put_line("[" & i'image & "] "
            & to_string(argument)
        );

        i := i + 1;
    end loop;
 exception
    when system.assertions.assert_failure =>
        ada.text_io.put_line("Failed precondition");
 end main;

Upvotes: 3

Views: 202

Answers (2)

Anh Vo
Anh Vo

Reputation: 149

Since exception can not be handled in a declarative section, the action should be moved to a package similar to the one below. Then, call it from a exception handling block of the main procedure. So, your code will not terminate after handling the exception.

with Ada.Command_line;
package Util is
    --...
    function Command_Argument_Count return Natural
         with Pre => Ada.Command_Line.Argument_Count > 2;
    --...
end Util;


--...
Exception_Handling_Block:
begin
    while i <= Util.Command_Argument_Count loop
        argument := to_bounded_string(
            ada.command_line.argument(i)
        );

        ada.text_io.put_line("[" & i'image & "] "
            & to_string(argument)
        );

        i := i + 1;
     end loop;
exception
    when system.assertions.assert_failure =>
        ada.text_io.put_line("Failed precondition");
end Exception_Handling_Block;
--...

Upvotes: 1

jacob
jacob

Reputation: 4956

I've found my answer:

Exception handlers have an important restriction that you need to be careful about: Exceptions raised in the declarative section are not caught by the handlers of that block.

From: https://learn.adacore.com/courses/intro-to-ada/chapters/exceptions.html

Upvotes: 4

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