On Mar 13, 2008, at 2:42 AM, Alan W. Irwin wrote: > The other point I want to make concerns segfaults which are defined as > follows (by wikipedia): "A segmentation fault occurs when a program > attempts > to access a memory location that it is not allowed to access, or > attempts to > access a memory location in a way that is not allowed". > http://en.wikipedia.org/wiki/Access_violation gives several > straightforward > ways you can get those from C, but they miss the big one which is > memory > management issues (i.e., reading or writing beyond the alloc'd memory) > causing an indirect segfault. As I understand it such memory > management > issues do not directly cause a segfault, but they do cause you to > overwrite > neighbouring alloc'd areas, and when you attempt to use pointers > from those > overwritten areas, you end up accessing the wrong memory which > often, _but > not always_ causes a segfault.
Agreed, but the segfault occurs because I did not think to check the return value of the function pango_cairo_create_layout(). It should return a pointer to a PangoLayout, but when it fails, as it does in our test case, it returns NULL. The program crashes when this null pointer is passed to the next function which expects a valid PangoLayout pointer. I can add a test for this and the program will no longer segfault, but this does not solve the problem of why pango_cairo_create_layout() is failing in the first place. Presumably it is trying to tell us something with the message: (process:10860): GLib-GObject-WARNING **: cannot register existing type `PangoCairoFcFontMap' Or maybe this could just mean that at some other point we are overwriting some crucial bit of memory? Unfortunately I have not been able to trigger this bug using a simple cairo/pango program that contains just the apparently problematic function calls. -Hazen ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ _______________________________________________ Plplot-devel mailing list Plplot-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/plplot-devel
