[vtk-developers] DebugLeaks C++ expert issue?

[David Cole]

Is it built with the /GF compiler flag?

https://docs.microsoft.com/en-us/cpp/build/reference/gf-eliminate-duplicate-strings?view=vs-2017


On Mon, Jan 7, 2019 at 11:59 AM Ben Boeckel via vtk-developers
<vtk-developers at vtk.org> wrote:
>
> On Mon, Jan 07, 2019 at 11:39:17 -0500, Ken Martin via vtk-developers wrote:
> > On VS2017 Debug with DEBUG_LEAKS I'm seeing an odd issue. DebugLeaks is
> > complaining about vtkCommands being leaked because the two string literals
> > in the below code have different addresses (the string address is used in a
> > map type structure). Looking at DebugLeaks the only way this code would
> > work is if they have the same address. But I checked in the debugger and
> > they have different addresses.
> >
> > <snip>
> >
> > I can fix it by doing the following but wanted a c++ expert to weigh in,
> > was the original code OK? Is this a compiler compliance issue? Is the
> > proposed fix the right approach?
>
> I don't think the standard says anything about a string literal with the
> same content as another literal having to share an address. I'd expect
> that this is mainly optimization at the compiler or linker level. For
> example, this:
>
>     const char* foo = "foobar";
>     const char* bar = "bar";
>
> can be satisfied with this in the resulting binary:
>
>     "foobar\0"
>      ^  ^
>      |  bar
>      foo
>
> but I'd expect the standard to say that doing `foo < bar` is always
> undefined behavior since they're not pointers to the same object.
>
> > const char *cname = "vtkCommand or subclass";
> >
> > //----------------------------------------------------------------
> > vtkCommand::vtkCommand():AbortFlag(0),PassiveObserver(0)
> > {
> > #ifdef VTK_DEBUG_LEAKS
> > vtkDebugLeaks::ConstructClass(cname);
> > #endif
> > }
> >
> > //----------------------------------------------------------------
> > void vtkCommand::UnRegister()
> > {
> > int refcount = this->GetReferenceCount()-1;
> > this->SetReferenceCount(refcount);
> > if (refcount <= 0)
> > {
> > #ifdef VTK_DEBUG_LEAKS
> > vtkDebugLeaks::DestructClass(cname);
> > #endif
> > delete this;
> > }
> > }
>
> This looks reasonable to me. Maybe add `static`?
>
> --Ben
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