Thank you Enrico and Zachary, I've updated my nullpointer checking code as follows.
def IsNullPtr(ptr): if ptr.GetType().IsPointerType() and ptr.GetValueAsUnsigned() == 0: return True; else: return False; That looks much more stable now. I hope someone reads this thread and corrects the example to fix the null pointer checks. -S On Mon, Feb 16, 2015 at 10:44 AM, Enrico Granata <egran...@apple.com> wrote: > > On Feb 16, 2015, at 10:11 AM, Zachary Turner <ztur...@google.com> wrote: > > The issue is that the example on the website is broken because it checks > GetValue() == None. So either the example is wrong > > > I would posit that the example is wrong - I don’t think anyone updated it > in the longest time, definitely not me > > or the implementation is wrong. Checking GetValue() against None is the > intuitive thing one would do though, so it seems desirable to make that work > > > I disagree. > > In our API, generally, an answer of None means “could not compute this” - > for instance, your SBValue refers to a variable that is out of scope, or is > outright invalid > Conflating the case of “I could compute this, the answer is 0” with “I > could not compute this” feels wrong - also, imagining this from the > perspective of, say, an IDE, it makes for more convoluted code: > > value = obj.GetValue() > if value == None: > if value.IsValid(): value = “NULL” #argh - None now means two things!!!!! > > I would also recommend against GetValue() for numeric comparisons - I > think even right now, that API returns “NULL” the string for null pointers > and “nil” for the ObjC version thereof - and if we could reliably tell C++ > >= 11, I would have no objection to making it return “nullptr” when > applicable > If you need a numeric value to compare - GetValueAsSigned/Unsigned() are > the APIs to go to - and even those should NOT return None to mean NULL, but > the correct bit pattern to mean NULL on the underlying system (which we are > assuming to be 0 :-) > > On Mon, Feb 16, 2015 at 9:19 AM Enrico Granata <egran...@apple.com> wrote: > > I may be clearly misunderstanding what you are trying to say here, but my >> expectation is that given >> >> T *ptr = nullptr; >> >> the way to check if "ptr" is a nullptr would be >> >> sbvalueForPtr.GetValueAsUnsigned() == 0 >> >> given that sbvalueForPtr.GetType().IsPointerType() is true >> >> As for the special case of a shared_ptr<>, that is a class that has an >> instance variable of pointer type. To check for NULL-ness, you're gonna >> have to retrieve the child. That requires you to have some knowledge of the >> internals of your standard C++ library. >> >> An alternative would be (and I am not sure if that is plugged in at the >> moment - if not feel free to ask for it, or provide a patch to that effect) >> to use the recently added ability for synthetic children to provide a >> numeric value. One could imagine wiring things up so that the >> shared_ptr<>'s value is the underlying pointer value. Then no child >> fetching would be required. >> >> Sent from my iPhone >> >> On Feb 15, 2015, at 11:23 PM, Spundun Bhatt <spun...@gmail.com> wrote: >> >> (Using OSX 10.10.1, XCode 6.1.1 6A2008a, lldb-320.4.156, Apple LLVM >> version 6.0 (clang-600.0.56) (based on LLVM 3.5svn) ) >> >> Hi all, >> I have just started using LLDB and its Python scripting interface. >> >> I may have stumbled upon a deep bug related to null pointer treatment. >> >> http://lldb.llvm.org/scripting.html I tried to follow this scripting >> tutorial. >> >> http://pastebin.com/S0RhVG3s This is the output of my interaction with >> the lldb and the python script. (I haven't modified any part of the example >> code there) >> >> It seems like `if left_child_ptr.GetValue() == None:` expression (and >> other similar expressions) doesn't evaluate to true for null pointers >> >> I was able to cook up a python check for null pointer: >> >> def IsNullPtr(ptr): >> >> ptr_string = str(ptr.GetValue()) >> >> if re.search('[1-9a-fA-F]', ptr_string): >> >> return False; >> >> else: >> >> return True; >> >> I discussed this on the irc channel and zturner thought it looked like a >> bug and that I should post it here. >> >> Hope this helps. >> Please let me know if there is a standard way to do null pointer check >> through the python API. Especially a check for nullptr shared_ptrs. >> >> _______________________________________________ >> lldb-dev mailing list >> lldb-dev@cs.uiuc.edu >> http://lists.cs.uiuc.edu/mailman/listinfo/lldb-dev >> >> _______________________________________________ >> lldb-dev mailing list >> lldb-dev@cs.uiuc.edu >> http://lists.cs.uiuc.edu/mailman/listinfo/lldb-dev >> > > Thanks, > *- Enrico* > [image: 📩] egranata@.com ☎️ 27683 > > > > >
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