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Re: Why gdb inside emacs cannot print out c++ object?


From: Kevin Gao
Subject: Re: Why gdb inside emacs cannot print out c++ object?
Date: Sat, 16 Mar 2019 17:57:36 -0700

For now, I use gdb command "info locals" as workaround. which is able to
print out C++ objects. etc it prints out


*m = std::map with 1 element = {["aaa"] = "bbb"}*
*p = {first = "aaa", second = "bbb"}*

I wish emacs gud window, locals cannot show the same thing.

Thanks,
Kevin


On Sat, Mar 16, 2019 at 5:48 PM Kevin Gao <address@hidden> wrote:

> Thanks, the original problem has gone away.
>
> About the link you shared:
>
> etc this code.
>
> *#include <map>*
> *#include <string>*
> *int main() {*
> *    std::map<std::string, std::string> m = {{"aaa", "bbb"}};*
> *    auto p = m.begin();*
> *    return 0;*
> *}*
>
> gdb in emacs can print the value which "p" points. gdb prints out "*$1 =
> {first = "aaa", second = "bbb"}*"
>
> Emacs speedbar can show the value correctly. Speedbar shows "*p {first =
> "aaa", second = "bbb"}*'
>
> The issue is: gud -> locals window cannot show the value correctly. It
> shows
> *std::_Rb_tree_iterator<std::pair<std::__cxx11::basic_string<char,
> std::char_traits<char>, std::allocator<char> > const,
> std::__cxx11::basic_string<char, std::char_traits<char>,
> std::allocator<char> > > >   p <complex data type>*
>
> Do you know if it is possible for locals window to show correct value
> which p points to? locals windows is more handy than gdb command and emacs
> speedbar.
>
> Thanks,
> Kevin
>
>
> On Sat, Mar 16, 2019 at 1:17 AM Eli Zaretskii <address@hidden> wrote:
>
>> > From: Kevin Gao <address@hidden>
>> > Date: Fri, 15 Mar 2019 16:46:30 -0700
>> > Cc: address@hidden
>> >
>> > Seems sth wrong with my machine. Sorry for the false report.
>>
>> So the problem went away somehow?
>>
>> > May I ask a related question? In the local windows, instead of showing
>> the value, it shows "<complex data
>> > type>". Is it possible to show the value of c++ object? (eg a
>> std::map's value)
>>
>> I think in these cases you need to provide your own pretty-printer.
>> See the node "Pretty Printing" in the GDB manual.  Looks like the GCC
>> folks already wrote such pretty-printers, see this stackoverflow
>> discussion:
>>
>>
>> https://stackoverflow.com/questions/11606048/how-to-pretty-print-stl-containers-in-gdb
>>
>>


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