[lldb-dev] Possible bug in the LLDB Python Scripting Example (And the API itself)

[Enrico Granata]

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 <spundun at 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.
> 
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