[lldb-dev] How to deal with STL type names in C++ code?

Thu Aug 6 15:50:08 PDT 2015

On Thu, Aug 6, 2015 at 3:38 PM, Enrico Granata <egranata at apple.com> wrote:

>
> On Aug 6, 2015, at 3:33 PM, Siva Chandra <sivachandra at google.com> wrote:
>
>
>
> On Thu, Aug 6, 2015 at 2:43 PM, Enrico Granata <egranata at apple.com> wrote:
>
>> To be honest, my favorite approach would be to modify clang’s TypePrinter
>> to do this, and then hooking up GetDisplayTypeName() to use whatever flags
>> would be necessary to invoke that bit of magic
>>
>
> Do you mean that clang's "pretty printer" should be made extensible by a
> script?
>
>
>
> Nope, what I am imagining is not an extensible system
>
> When LLDB goes to print a type it asks the compiler “what is the name of
> this type that I should display?”
> By default, clang prints the fully specialized template, including type
> arguments that have their default value. My theory is that we would want to
> add a mode to the type printer to say “simplify type name”, and that would
> do sensible things to get a display name that is more compact
>

So, how would clang know about the "simplified" or "friendly" name for a
type? Even in case of standard library types, the underlying types (with
unfriendly type names) could be anything. For example, libstdc++ and
STLport have different underlying naming conventions. So does libc++ I
would imagine (I have not spent enough time yet staring at libc++ code).

>
> That seems more interesting than a set of regular expression heuristics on
> the type name, which is probably all you could do without specialized
> compiler-*y* knowledge of types
>

>
>> On Aug 6, 2015, at 2:33 PM, Siva Chandra <sivachandra at google.com> wrote:
>>
>> FWIW, GDB has a similar concept called type-printers:
>> https://sourceware.org/gdb/current/onlinedocs/gdb/Type-Printing-API.html
>>
>> On Thu, Aug 6, 2015 at 2:24 PM, Siva Chandra <sivachandra at google.com>
>> wrote:
>>
>> Hi Enrico,
>>
>> I was thinking about the same issue today. Could we add a concept
>> called "TypeNameModifier" and provide ability to define modifiers in
>> scripts and command line? With this, a name like
>> std::__1::basic_string<...> can be modified into a more friendly name
>> like std::string? We could ofcourse have more complex modifications.
>>
>> I think it is doable, but what is your (and the community's) opinion
>> about adding such a feature? If you are OK, I would like to take up
>> adding such a feature.
>>
>> Thanks,
>> Siva Chandra
>>
>> On Thu, Aug 6, 2015 at 2:15 PM, Enrico Granata via lldb-dev
>> <lldb-dev at lists.llvm.org> wrote:
>>
>> Hi Eugene,
>>
>> On Aug 6, 2015, at 2:02 PM, Eugene Birukov via lldb-dev
>> <lldb-dev at lists.llvm.org> wrote:
>>
>> Hi,
>>
>> I am using LLDB C++ API to create custom debugger and trying to dump
>> variables with their types. To do that I am using SBValue.GetTypeName()
>> API.
>> Some types are OK, but some others - especially ones related to STL - are
>> quite unreadable:
>>
>>
>> those type names are the actual fully-specialized STL type names. I am not
>> sure how to control GDB to stop truncating your string formatting, but
>> after
>> the “…” there actually is more text
>> It looks like what you have is std::unique_ptr<std::vector<std::string> >
>> >
>> and those templates all take more arguments which are defaulted so you
>> don’t
>> have to type them in code - but are reflected in the type name
>>
>> (gdb) p value.GetTypeName()
>> $1 = 0x7fffe419be40
>> "std::__1::unique_ptr<std::__1::vector<std::__1::basic_string<char,
>> std::__1::char_traits<char>, std::__1::allocator<char> >,
>> std::__1::allocator<std::__1::basic_string<char,
>> std::__1::char_traits<char"...
>> (gdb) p value.GetDisplayTypeName()
>> $2 = 0x7fffe419be40
>> "std::__1::unique_ptr<std::__1::vector<std::__1::basic_string<char,
>> std::__1::char_traits<char>, std::__1::allocator<char> >,
>> std::__1::allocator<std::__1::basic_string<char,
>> std::__1::char_traits<char"...
>> (gdb)
>>
>>
>> So, is there any way to convert them into some more human-friendly form?
>>
>>
>> Not currently. What one would have to do is hook into the C++ type
>> printing
>> logic such that it would know to leave out these extra template arguments
>> when they have a default value
>>
>>
>> Thanks,
>> Eugene
>> _______________________________________________
>> lldb-dev mailing list
>> lldb-dev at lists.llvm.org
>> http://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-dev
>>
>>
>>
>> Thanks,
>> - Enrico
>> 📩 egranata@.com ️ 27683
>>
>>
>> _______________________________________________
>> lldb-dev mailing list
>> lldb-dev at lists.llvm.org
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>>
>>
>>
>> Thanks,
>> *- Enrico*
>> 📩 egranata@.com ☎️ 27683
>>
>>
>
>
> Thanks,
> *- Enrico*
> 📩 egranata@.com ☎️ 27683
>
>
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