Bug 36020

Summary: Context::set_dash throws "vector subscript out of range" on VS2008
Product: cairomm Reporter: Robert Kurjata <rkurjata>
Component: GeneralAssignee: Murray Cumming <murrayc>
Status: RESOLVED FIXED QA Contact:
Severity: major    
Priority: medium    
Version: unspecified   
Hardware: Other   
OS: Windows (All)   
Whiteboard:
i915 platform: i915 features:

Description Robert Kurjata 2011-04-06 01:16:04 UTC 
Setting dash to empty requires passing of an empty vector.

In VisualStudio 2008 an exception is thrown due to dereference of first element of an empty vector, which is not allowed (in GCC it is allowed, and code below works correctly). This applies to debug and release builds with default SCL_SECURE configuration.

void Context::set_dash(std::vector<double>& dashes, double offset)
{
  cairo_set_dash(cobj(), &dashes[0], dashes.size(), offset);
  check_object_status_and_throw_exception(*this);
}

a proposed solution is to add specific check

void Context::set_dash(std::vector<double>& dashes, double offset)
{
  cairo_set_dash(cobj(), dashes.size()?&dashes[0]:NULL, dashes.size(), offset);
  check_object_status_and_throw_exception(*this);
}

The same is applicable for const version of the function.

This fixes issue for me.

Interesting discusion of this problem can be found at:
http://stackoverflow.com/questions/3829788/using-operator-on-empty-stdvector
Comment 1 Murray Cumming 2014-01-28 12:18:56 UTC 
Sorry for the very late reply.

You are quite right. We should be checking these vectors before derefencing them. I have done that in that method and a few others:
http://cgit.freedesktop.org/cairomm/commit/?id=798a292d2ec0c05e6ccf9108c6a973651a3ddcfe

The functions are not explicitly documented as accepting NULL for these parameters, but it seems like it should be OK, as long as the size is 0.

Thanks.

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