Re: goocanvasmm: problem on accessing cairo matrix
- From: Murray Cumming <murrayc murrayc com>
- To: David questans co uk
- Cc: gtkmm-list gnome org
- Subject: Re: goocanvasmm: problem on accessing cairo matrix
- Date: Tue, 14 Jul 2009 12:42:14 +0200
On Mon, 2009-07-13 at 18:28 +0100, David Davies wrote:
> void ExampleWindow::update_label()
> cairo_matrix_t * pMatrix = m_text->property_transform(); // line A
> double x0 = pMatrix->x0; // line B
> std::stringstream str;
> My aim is to output the components of the transform matrix so that I
> understand what is happening to it.
> The program compiles and links in CDT with no reported error.
> If I comment out line B, it runs OK and, as expected, gives the same
> output as the original example.
> With line B however, the program terminates and outputs a
> message without opening a window.
> It does not report an error.
You really need to use a debugger. I suspect that pMatrix is null. You
should check pointers for null before dereferencing them anyway.
I don't know _why_ it is null. Maybe that's a normal value, if there is
no "transformation matrix" set for the item, though I don't quite know
when that would be set.
murrayc murrayc com
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