Re: [boost] boost::exception questions

From: Emil Dotchevski (emil_at_[hidden])
Date: 2007-09-30 21:55:01

> <snip>
> I see. This feature is most valuable. However, so is Tom's suggestion
> and I don't think both are mutually exclusive (that is if we let go of
> using the template-id 'error_info' for the latter):
>
>      typedef boost::custom_exception<tag::
>          errno,tag::filename,tag::size> file_error;

Consider this code:

void read_file( char const * filename )
{
    something_unrelated();
    ....
    if( file_failure )
        throw file_error() << error_info<tag_filename>(filename);
}

If I understand correctly, you are concerned with making sure all
file_error exceptions pack a file_name.

But what if "something_unrelated" throws? Isn't the filename known to
our function relevant to that other failure too? It sure is, despite
that we have no idea what exceptions "something_unrelated" could
throw.

So, I'd write that function like this:

void read_file( char const * filename )
{
    try
    {
        something_unrelated();
        ....
        if( file_failure )
            throw file_error();
    }
    catch( boost::exception & x )
    {
        x << error_info<tag_filename>(filename);
        throw;
    }
}

How would your custom_exception idea fit in this framework?

Emil Dotchevski