Workaround GCC 5.5 unordered_map bug - c++

Question

This code works in GCC 6.1, but causes a compile error in GCC 5.5:
#include <memory>
#include <unordered_map>
#include <vector>
std::unordered_map<int, std::shared_ptr<std::vector<uint8_t>>> foo;
int main() {
foo.emplace(0, new std::vector<uint8_t>(1));
}
The error is below. Is there any way around this (I assume) bug?
In file included from /opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/x86_64-linux-gnu/bits/c++allocator.h:33:0,
from /opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/bits/allocator.h:46,
from /opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/memory:63,
from <source>:1:
/opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/ext/new_allocator.h: In instantiation of 'void
__gnu_cxx::new_allocator<_Tp>::construct(_Up*, _Args&& ...) [with _Up = std::pair<const int, std::shared_ptr<std::vector<unsigned char> > >; _Args = {int, std::vector<unsigned char, std::allocator<unsigned char> >*}; _Tp = std::pair<const int, std::shared_ptr<std::vector<unsigned char> > >]':
/opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/bits/alloc_traits.h:530:4: required from 'static void std::allocator_traits<std::allocator<_Tp1>
>::construct(std::allocator_traits<std::allocator<_Tp1> >::allocator_type&, _Up*, _Args&& ...) [with _Up = std::pair<const int, std::shared_ptr<std::vector<unsigned char> > >; _Args = {int, std::vector<unsigned char, std::allocator<unsigned char> >*}; _Tp = std::pair<const int, std::shared_ptr<std::vector<unsigned char> > >; std::allocator_traits<std::allocator<_Tp1> >::allocator_type = std::allocator<std::pair<const int, std::shared_ptr<std::vector<unsigned char> > > >]'
/opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/bits/hashtable_policy.h:1955:37: required from 'std::__detail::_Hashtable_alloc<_NodeAlloc>::__node_type* std::__detail::_Hashtable_alloc<_NodeAlloc>::_M_allocate_node(_Args&& ...) [with _Args = {int, std::vector<unsigned char, std::allocator<unsigned char> >*}; _NodeAlloc = std::allocator<std::__detail::_Hash_node<std::pair<const int, std::shared_ptr<std::vector<unsigned char> > >, false> >; std::__detail::_Hashtable_alloc<_NodeAlloc>::__node_type = std::__detail::_Hash_node<std::pair<const int, std::shared_ptr<std::vector<unsigned char> > >, false>]'
/opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/bits/hashtable.h:1517:77: required from 'std::pair<typename std::__detail::_Hashtable_base<_Key,
_Value, _ExtractKey, _Equal, _H1, _H2, _Hash, _Traits>::iterator, bool> std::_Hashtable<_Key, _Value, _Alloc, _ExtractKey, _Equal, _H1,
_H2, _Hash, _RehashPolicy, _Traits>::_M_emplace(std::true_type, _Args&& ...) [with _Args = {int, std::vector<unsigned char, std::allocator<unsigned char> >*}; _Key = int; _Value = std::pair<const int, std::shared_ptr<std::vector<unsigned char> > >;
_Alloc = std::allocator<std::pair<const int, std::shared_ptr<std::vector<unsigned char> > > >; _ExtractKey = std::__detail::_Select1st; _Equal = std::equal_to<int>; _H1 = std::hash<int>; _H2 = std::__detail::_Mod_range_hashing; _Hash = std::__detail::_Default_ranged_hash; _RehashPolicy = std::__detail::_Prime_rehash_policy; _Traits = std::__detail::_Hashtable_traits<false, false, true>; typename std::__detail::_Hashtable_base<_Key, _Value, _ExtractKey, _Equal, _H1,
_H2, _Hash, _Traits>::iterator = std::__detail::_Node_iterator<std::pair<const int, std::shared_ptr<std::vector<unsigned char> > >, false, false>; std::true_type = std::integral_constant<bool, true>]'
/opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/bits/hashtable.h:726:21: required from 'std::_Hashtable<_Key, _Value, _Alloc, _ExtractKey,
_Equal, _H1, _H2, _Hash, _RehashPolicy, _Traits>::__ireturn_type std::_Hashtable<_Key, _Value, _Alloc, _ExtractKey, _Equal, _H1, _H2,
_Hash, _RehashPolicy, _Traits>::emplace(_Args&& ...) [with _Args = {int, std::vector<unsigned char, std::allocator<unsigned char> >*};
_Key = int; _Value = std::pair<const int, std::shared_ptr<std::vector<unsigned char> > >; _Alloc = std::allocator<std::pair<const int, std::shared_ptr<std::vector<unsigned char> > > >; _ExtractKey = std::__detail::_Select1st; _Equal = std::equal_to<int>; _H1 = std::hash<int>; _H2 = std::__detail::_Mod_range_hashing; _Hash = std::__detail::_Default_ranged_hash; _RehashPolicy = std::__detail::_Prime_rehash_policy; _Traits = std::__detail::_Hashtable_traits<false, false, true>; std::_Hashtable<_Key, _Value, _Alloc, _ExtractKey, _Equal, _H1, _H2,
_Hash, _RehashPolicy, _Traits>::__ireturn_type = std::pair<std::__detail::_Node_iterator<std::pair<const int, std::shared_ptr<std::vector<unsigned char> > >, false, false>, bool>]'
/opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/bits/unordered_map.h:380:54: required from 'std::pair<typename std::_Hashtable<_Key, std::pair<const _Key, _Tp>, _Alloc, std::__detail::_Select1st, _Pred,
_Hash, std::__detail::_Mod_range_hashing, std::__detail::_Default_ranged_hash, std::__detail::_Prime_rehash_policy, std::__detail::_Hashtable_traits<std::__not_<std::__and_<std::__is_fast_hash<_Hash>, std::__detail::__is_noexcept_hash<_Key, _Hash> > >::value, false, true> >::iterator, bool> std::unordered_map<_Key, _Tp, _Hash, _Pred,
_Alloc>::emplace(_Args&& ...) [with _Args = {int, std::vector<unsigned char, std::allocator<unsigned char> >*}; _Key = int; _Tp = std::shared_ptr<std::vector<unsigned char> >; _Hash = std::hash<int>;
_Pred = std::equal_to<int>; _Alloc = std::allocator<std::pair<const int, std::shared_ptr<std::vector<unsigned char> > > >; typename std::_Hashtable<_Key, std::pair<const _Key, _Tp>, _Alloc, std::__detail::_Select1st, _Pred, _Hash, std::__detail::_Mod_range_hashing, std::__detail::_Default_ranged_hash, std::__detail::_Prime_rehash_policy, std::__detail::_Hashtable_traits<std::__not_<std::__and_<std::__is_fast_hash<_Hash>, std::__detail::__is_noexcept_hash<_Key, _Hash> > >::value, false, true> >::iterator = std::__detail::_Node_iterator<std::pair<const int, std::shared_ptr<std::vector<unsigned char> > >, false, false>]'
<source>:8:47: required from here
/opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/ext/new_allocator.h:120:4: error: no matching function for call to 'std::pair<const int, std::shared_ptr<std::vector<unsigned char> > >::pair(int, std::vector<unsigned char>*)'
{ ::new((void *)__p) _Up(std::forward<_Args>(__args)...); }
^
In file included from /opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/bits/stl_algobase.h:64:0,
from /opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/memory:62,
from <source>:1:
/opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/bits/stl_pair.h:206:9: note: candidate: template<class ... _Args1, long unsigned int ..._Indexes1, class ... _Args2, long unsigned int ..._Indexes2> std::pair<_T1, _T2>::pair(std::tuple<_Args1 ...>&, std::tuple<_Args2 ...>&, std::_Index_tuple<_Indexes1 ...>, std::_Index_tuple<_Indexes2 ...>)
pair(tuple<_Args1...>&, tuple<_Args2...>&,
^
/opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/bits/stl_pair.h:206:9: note: template argument deduction/substitution failed:
In file included from /opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/x86_64-linux-gnu/bits/c++allocator.h:33:0,
from /opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/bits/allocator.h:46,
from /opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/memory:63,
from <source>:1:
/opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/ext/new_allocator.h:120:4: note: mismatched types 'std::tuple<_Elements ...>' and 'int'
{ ::new((void *)__p) _Up(std::forward<_Args>(__args)...); }
^
In file included from /opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/bits/stl_algobase.h:64:0,
from /opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/memory:62,
from <source>:1:
/opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/bits/stl_pair.h:155:9: note: candidate: template<class ... _Args1, class ... _Args2> std::pair<_T1, _T2>::pair(std::piecewise_construct_t, std::tuple<_Args1 ...>, std::tuple<_Args2 ...>)
pair(piecewise_construct_t, tuple<_Args1...>, tuple<_Args2...>);
^
/opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/bits/stl_pair.h:155:9: note: template argument deduction/substitution failed:
In file included from /opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/x86_64-linux-gnu/bits/c++allocator.h:33:0,
from /opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/bits/allocator.h:46,
from /opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/memory:63,
from <source>:1:
/opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/ext/new_allocator.h:120:4: note: cannot convert 'std::forward<int>((* & __args#0))' (type 'int') to type 'std::piecewise_construct_t'
{ ::new((void *)__p) _Up(std::forward<_Args>(__args)...); }
^
In file included from /opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/bits/stl_algobase.h:64:0,
from /opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/memory:62,
from <source>:1:
/opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/bits/stl_pair.h:150:12: note: candidate: template<class _U1, class _U2, class> constexpr std::pair<_T1, _T2>::pair(std::pair<_U1, _U2>&&)
constexpr pair(pair<_U1, _U2>&& __p)
^
/opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/bits/stl_pair.h:150:12: note: template argument deduction/substitution failed:
In file included from /opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/x86_64-linux-gnu/bits/c++allocator.h:33:0,
from /opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/bits/allocator.h:46,
from /opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/memory:63,
from <source>:1:
/opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/ext/new_allocator.h:120:4: note: mismatched types 'std::pair<_T1, _T2>' and 'int'
{ ::new((void *)__p) _Up(std::forward<_Args>(__args)...); }
^
In file included from /opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/bits/stl_algobase.h:64:0,
from /opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/memory:62,
from <source>:1:
/opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/bits/stl_pair.h:144:12: note: candidate: template<class _U1, class _U2, class> constexpr std::pair<_T1, _T2>::pair(_U1&&, _U2&&)
constexpr pair(_U1&& __x, _U2&& __y)
^
/opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/bits/stl_pair.h:144:12: note: template argument deduction/substitution failed:
/opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/bits/stl_pair.h:141:38: error: no type named 'type' in 'struct std::enable_if<false, void>'
template<class _U1, class _U2, class = typename
^
/opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/bits/stl_pair.h:138:12: note: candidate: template<class _U2, class> constexpr std::pair<_T1,
_T2>::pair(const _T1&, _U2&&)
constexpr pair(const _T1& __x, _U2&& __y)
^
/opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/bits/stl_pair.h:138:12: note: template argument deduction/substitution failed:
/opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/bits/stl_pair.h:136:27: error: no type named 'type' in 'struct std::enable_if<false, void>'
template<class _U2, class = typename
^
/opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/bits/stl_pair.h:133:12: note: candidate: template<class _U1, class> constexpr std::pair<_T1,
_T2>::pair(_U1&&, const _T2&)
constexpr pair(_U1&& __x, const _T2& __y)
^
/opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/bits/stl_pair.h:133:12: note: template argument deduction/substitution failed:
In file included from /opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/x86_64-linux-gnu/bits/c++allocator.h:33:0,
from /opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/bits/allocator.h:46,
from /opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/memory:63,
from <source>:1:
/opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/ext/new_allocator.h:120:4: note: cannot convert 'std::forward<std::vector<unsigned char>*>((* &
__args#1))' (type 'std::vector<unsigned char>*') to type 'const std::shared_ptr<std::vector<unsigned char> >&'
{ ::new((void *)__p) _Up(std::forward<_Args>(__args)...); }
^
In file included from /opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/bits/stl_algobase.h:64:0,
from /opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/memory:62,
from <source>:1:
/opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/bits/stl_pair.h:128:17: note: candidate: constexpr std::pair<_T1, _T2>::pair(std::pair<_T1,
_T2>&&) [with _T1 = const int; _T2 = std::shared_ptr<std::vector<unsigned char> >]
constexpr pair(pair&&) = default;
^
/opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/bits/stl_pair.h:128:17: note: candidate expects 1 argument, 2 provided
/opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/bits/stl_pair.h:127:17: note: candidate: constexpr std::pair<_T1, _T2>::pair(const std::pair<_T1, _T2>&) [with _T1 = const int; _T2 = std::shared_ptr<std::vector<unsigned char> >]
constexpr pair(const pair&) = default;
^
/opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/bits/stl_pair.h:127:17: note: candidate expects 1 argument, 2 provided
/opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/bits/stl_pair.h:124:12: note: candidate: template<class _U1, class _U2, class> constexpr std::pair<_T1, _T2>::pair(const std::pair<_U1, _U2>&)
constexpr pair(const pair<_U1, _U2>& __p)
^
/opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/bits/stl_pair.h:124:12: note: template argument deduction/substitution failed:
In file included from /opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/x86_64-linux-gnu/bits/c++allocator.h:33:0,
from /opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/bits/allocator.h:46,
from /opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/memory:63,
from <source>:1:
/opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/ext/new_allocator.h:120:4: note: mismatched types 'const std::pair<_T1, _T2>' and 'int'
{ ::new((void *)__p) _Up(std::forward<_Args>(__args)...); }
^
In file included from /opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/bits/stl_algobase.h:64:0,
from /opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/memory:62,
from <source>:1:
/opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/bits/stl_pair.h:112:26: note: candidate: constexpr std::pair<_T1, _T2>::pair(const _T1&, const
_T2&) [with _T1 = const int; _T2 = std::shared_ptr<std::vector<unsigned char> >]
_GLIBCXX_CONSTEXPR pair(const _T1& __a, const _T2& __b)
^
/opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/bits/stl_pair.h:112:26: note: no known conversion for argument 2 from 'std::vector<unsigned char>*' to 'const std::shared_ptr<std::vector<unsigned char> >&'
/opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/bits/stl_pair.h:108:26: note: candidate: constexpr std::pair<_T1, _T2>::pair() [with _T1 = const int; _T2 = std::shared_ptr<std::vector<unsigned char> >]
_GLIBCXX_CONSTEXPR pair()
^
/opt/compiler-explorer/gcc-5.5.0/include/c++/5.5.0/bits/stl_pair.h:108:26: note: candidate expects 0 arguments, 2 provided
Compiler returned: 1

Answer 1

Use std::make_shared:
foo.emplace(0, std::make_shared<std::vector<uint8_t>>(1));
live example on wandbox.org

Answer 2

In C++11 the emplace method for map and unordered_map was cumbersome. By default it actually needs to be fed the construction parameters for the std::pair used for the insert method.
In c++17, I think, this is improved, so you can provide 2 arguments, and the second argument is only applied if the object is actually emplaced.
Meanwhile, back in C++11 you are forced to use the piecewise mechanism if you really want to insert objects on demand. C++11 emplace example
However, in your case, my main concern is that the new object is already built and might leak if it already has an index in the map, and does not get inserted. Using make_shared helps avoid that issue, at least!