c++ - SEGV in gcc's std::unordered_map -

i have encountered segv in gcc 4.7.2's unordered_map

in find() calls _m_find_node, in turn calls _m_find_before_node, passing in bucket number, key we're searching for, , hash code.

in _m_find_before_node, looks first node in bucket in question:

_basenode* __prev_p = _m_buckets[__n]; 

and gets node following this:

_node* __p = static_cast<_node*>(__prev_p->_m_nxt); 

the problem __prev_p->_m_nxt null; , _m_equals tries dereference , causes seg fault.

i'm not 100% clued on inner workings of unordered_map - requirement first node in bucket's _m_nxt non-null, or bug?

the code in question here:

  // find node key compares equal k in bucket n. return nullptr   // if no node found.   template<typename _key, typename _value,        typename _allocator, typename _extractkey, typename _equal,        typename _h1, typename _h2, typename _hash, typename _rehashpolicy,        bool __chc, bool __cit, bool __uk>     typename _hashtable<_key, _value, _allocator, _extractkey,             _equal, _h1, _h2, _hash, _rehashpolicy,             __chc, __cit, __uk>::_basenode*     _hashtable<_key, _value, _allocator, _extractkey, _equal,            _h1, _h2, _hash, _rehashpolicy, __chc, __cit, __uk>::     _m_find_before_node(size_type __n, const key_type& __k,             typename _hashtable::_hash_code_type __code) const     {       _basenode* __prev_p = _m_buckets[__n];       if (!__prev_p)     return nullptr;       _node* __p = static_cast<_node*>(__prev_p->_m_nxt); // __p null here!!       (;; __p = __p->_m_next())     {       if (this->_m_equals(__k, __code, __p))         return __prev_p;       if (!(__p->_m_nxt) || _m_bucket_index(__p->_m_next()) != __n)         break;       __prev_p = __p;     }       return nullptr;     } 

i'm not 100% clued on inner workings of unordered_map - requirement first node in bucket's _m_nxt non-null, or bug?

the question specific gcc's implementation, i'm pretty sure if _m_buckets[__n] non-null _m_buckets[__n]->_m_nxt should non-null too.

i.e. if bucket empty _m_buckets[__n]==nullptr, if bucket non-empty _m_buckets[__n]->_m_nxt first node in bucket.

try building -d_glibcxx_debug , see if identifies problem code, it's possible there's bug it's more you've corrupted container somehow or using wrong.