[cairo] cairomm exception handling questions
murrayc at murrayc.com
Mon Aug 11 10:42:05 PDT 2008
On Mon, 2008-08-11 at 09:56 -0300, Ian Britten wrote:
> Hi all,
> Just a couple of elementary exception handling questions, related
> to cairomm. (I'm trying to get my groundwork laid correctly)
> - After some trial-and-error (And grubbing through the cairomm
> source code), I've discovered that passing an invalid file name
> to PdfSurface::create() doesn't throw a Cairo::logic_error
> exception, but instead, a std::ios_base::failure exception.
As you can see in the implementation here:
this is the (indirectly) recommended exception for this cairo error:
But if we are wrong about that, changing the exceptions thrown would
generally be an API and ABI break - applications that expected the
existing exceptions would no longer work.
> Wouldn't it make it more consistent to throw all cairomm
> exceptions as Cairo::logic_error? Currently, I (as a programmer
> trying to trap all Cairo exceptions and downgrading them to
> errors) must add multiple 'catch' statements to all my 'try'
> statements. That seems like it'll get repetitive/tedious pretty
> quickly.. :(
Of course you shouldn't be catching the exceptions for every call.
That's why they are exceptions. But yes, I can see how it's a bit
annoying to have to catch more than one exception type.
I think it's more important that we document what exceptions can be
thrown by what methods. But to know that we need to know what errors can
be set by what C functions and that's lacking from the cairo
documentation currently. For instance:
> - What am I expected to do with a Cairo::logic_error exception? I
> had been planning to try use the ErrorStatus (cairo_status_t) to
> return a meaningful error to the calling code. However, it seems
> that I can't access the status (private, no 'get').
Good point. I guess there should be a get_error_code() method. A patch
would be welcome.
> Thus, it
> seems that all I can do is return a "Something went wrong in Cairo"
> error, from every 'catch' that I write...
> Thanks for any info, and sorry if I've missed something basic! I'm
> just trying to make sure I get off on the right foot!
murrayc at murrayc.com
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