Improved pretty printing for smart pointers

[Michael Marte]

Hi Jonathan,

I know that there are ways to dereference a smart pointer on the gdb 
command line. But when using an IDE (like Eclipse CTD, Qt Creator or 
kdevelop), the pretty printer, in its current state, is in the way: The 
variable view of the debugger will show a message like

"std::shared_ptr (count 1, weak 0) 0x61e1a8"

and then you are stuck because there is no way to inspect the members of 
the smart pointer. Of course there are workarounds (like all of the 
above mentioned IDEs give access to the gdb command line and both 
Eclipse CTD and Qt Creator support user-defined expressions, but 
kdevelop does not, as it seems) but these workarounds are tedious and 
make the browsing of large data structures painful.

I have not yet submitted a GCC copyright assignment to the FSF. Is this 
necessary for a minor addition to an optional add-on?

Michael


On 04/24/2013 09:48 AM, Jonathan Wakely wrote:
> On 24 April 2013 07:08, Michael Marte wrote:
>> Hello *,
>>
>> I found the pretty printers for std::shared_ptr, std::weak_ptr and
>> std::unique_ptr (as provided by
>> svn://gcc.gnu.org/svn/gcc/trunk/libstdc++-v3/python) not sufficient for
>> daily use as they only generate a description (including the address of
>> the pointee) but do not pretty print the pointee itself. This behaviour
>> implies that one has to copy the address of the pointee, cast it to the
>> pointee's type, and dereference the result.
>
> Or you just say 'print *ptr' and GDB dereferences it for you, which is
> the same as a built-in pointer.
>
> This works for shared_ptr but not currently for unique_ptr, I'm not
> sure why, I'll look into that (I also want to improve the output for a
> unique_ptr with custom deleter)
>
> For weak_ptr, which has no dereference operator to use but you can say
> 'print *wptr._M_ptr' (and that works for shared_ptr too)
>
>
>> To improve on the current
>> state of affairs, I improved the pretty printers to generate children.
>> For std::shared_ptr and std::weak_ptr, three children are generated,
>> namely "Use count", "Weak count", and "Managed value". For
>> std::unique_ptr, one child is generated, namely "Managed value". Using
>> this solution with an IDE like kdevelop or Eclipse CTD, it only needs
>> two clicks to see the value managed by a smart pointer.
>
> I haven't checked what the output is, but I'm unsure about making this
> change. I like having the smart pointers behave basically like a
> built-in pointer.  If you want the value you can dereference the
> pointer.
>
>> I attached my patch in the hope that you will find it interesting and
>> that it will be integrated into the suite of GCC STL pretty printers.
>
> Do you have a GCC copyright assignment submitted to the FSF?  That is
> required before significant patches can be accepted. This might be
> small enough to not require it though.
>