Re: Initializing of vector<const string> fails - gcc bug?

From:

Bo Persson <bop@gmb.dk>

Newsgroups:

comp.lang.c++.moderated

Date:

Wed, 4 Dec 2013 12:58:17 CST

Message-ID:

<bg94qpFshcqU1@mid.individual.net>

Helmut Jarausch wrote 2013-12-04 14:07:

Hi,

I cannot initialize a vector of const string elements with gcc-4.8.2 -std=c++11
The example below will be compiled if 'const string' is replaced by 'string'.

Is this a gcc bug or a restriction of the C++11 standard?

It is perhaps not explicitly stated in the standard, but an effect of
the requirements for an allocator.

If the value_type of the container is const, among other things we get
problems with functions overloaded for const and non-const objects.

See below.

#include <string>
using std::string;

#include <vector>

int main() { // compiled with std=c++11 using gcc-4.8.2

   std::vector<const string> Labels= {"A","B"};
}

/* I have removed '/usr/lib/gcc/x86_64-pc-linux-gnu/4.8.2/include'
     at the beginning of the error messages below
In file included
from x86_64-pc-linux-gnu/bits/c++allocator.h:33:0,
from bits/allocator.h:46,
from string:41,
from Vector_init_const_string.C:1:
ext/new_allocator.h: In instantiation of
  'struct __gnu_cxx::new_allocator<const std::basic_string<char> >':
...
Vector_init_const_string.C:8:29:
    required from here
ext/new_allocator.h:93:7: error:
   'const _Tp* __gnu_cxx::new_allocator<_Tp>::
    address(__gnu_cxx::new_allocator<_Tp>::const_reference) const
       [with _Tp = const std::basic_string<char>;
       __gnu_cxx::new_allocator<_Tp>::const_pointer
       = const std::basic_string<char>*; __gnu_cxx::new_allocator<_Tp>::const_reference
       = const std::basic_string<char>&]' cannot be overloaded
        address(const_reference __x) const _GLIBCXX_NOEXCEPT

Here we get into trouble with const_reference and const_pointer when
they end up being the same type as plain reference and pointer (all of
them referring to a const string).

Bo Persson

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