Re: goocanvasmm: problem on accessing cairo matrix

[Murray Cumming <murrayc murrayc com>]

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;
>    ...
>    etc
> 
> My aim is to output the components of the transform matrix so that I
> can 
> 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
> <terminated> 
> 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.

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