c++ - 模棱两可的 map.insert in boost

Question

我正在尝试将一个值插入到 boost 映射中，但是在 boost 映射插入中对插入语句的调用不明确。

#include <boost/interprocess/managed_shared_memory.hpp>
#include <boost/interprocess/containers/map.hpp>
#include <boost/interprocess/allocators/allocator.hpp>
#include <functional>
#include <utility>

using namespace boost::interprocess;

    int main ()
    {

    // remove earlier existing SHM
    shared_memory_object::remove("SharedMemoryName");

    // create new
    managed_shared_memory segment(create_only,"SharedMemoryName",65536);

    //Note that map<Key, MappedType>'s value_type is std::pair<const Key, MappedType>,
    //so the allocator must allocate that pair.
    typedef std::string KeyType;
    typedef map<std::string, int>  MappedType;
    typedef std::pair<const KeyType, MappedType> ValueType;

    //allocator of for the map.
    typedef allocator<ValueType, managed_shared_memory::segment_manager> ShmemAllocator;


    //Initialize the shared memory STL-compatible allocator
    ShmemAllocator alloc_inst (segment.get_segment_manager());

    //third parameter argument is the ordering function is used to compare the keys.
    typedef map<KeyType, MappedType, std::less<KeyType>, ShmemAllocator> MySHMMap;

    //offset ptr within SHM for map
    offset_ptr<MySHMMap> m_pmap = segment.construct<MySHMMap>("MySHMMapName")(std::less<std::string>(), alloc_inst);

    //Insert data in the map
           std::string my_string = "test";
            m_pmap[0].insert(std::make_pair( my_string, 0) );


    return 0;
}

被调用的 boost API 是:

    std::pair<iterator,bool> insert(const nonconst_value_type& x)
    std::pair<iterator,bool> insert(const value_type& x)
    typedef typename tree_t::value_type             value_type;
    typedef std::pair<key_type, mapped_type>        nonconst_value_type;

错误日志:

/home/user/droy/src/quotes/shmmutimap/src/writer.cxx:39: error:  call of overloaded 'insert(std::pair<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, int>)' is ambiguous
/home/dev/build/third_party/64-rhel5/boost_1_47_0/include/boost/interprocess/containers/container/map.hpp:410: note: candidates are: std::pair<typename boost::container::containers_detail::rbtree<Key, std::pair<const Key, T>, boost::container::containers_detail::select1st<std::pair<const Key, T> >, Pred, Alloc>::iterator, bool> boost::container::map<Key, T, Pred, Alloc>::insert(const typename boost::container::containers_detail::rbtree<Key, std::pair<const Key, T>, boost::container::containers_detail::select1st<std::pair<const Key, T> >, Pred, Alloc>::value_type&) [with Key = std::basic_string<char, std::char_traits<char>, std::allocator<char> >, T = boost::container::map<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, int, std::less<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::pair<const std::basic_string<char, std::char_traits<char>, std::allocator<char> >, int> > >, Pred = std::less<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, Alloc = boost::interprocess::allocator<std::pair<const std::basic_string<char, std::char_traits<char>, std::allocator<char> >, boost::container::map<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, int, std::less<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::pair<const std::basic_string<char, std::char_traits<char>, std::allocator<char> >, int> > > >, boost::interprocess::segment_manager<char, boost::interprocess::rbtree_best_fit<boost::interprocess::mutex_family, boost::interprocess::offset_ptr<void>, 0ul>, boost::interprocess::iset_index> >]
/home/dev/build/third_party/64-rhel5/boost_1_47_0/include/boost/interprocess/containers/container/map.hpp:421: note:                 std::pair<typename boost::container::containers_detail::rbtree<Key, std::pair<const Key, T>, boost::container::containers_detail::select1st<std::pair<const Key, T> >, Pred, Alloc>::iterator, bool> boost::container::map<Key, T, Pred, Alloc>::insert(const std::pair<typename boost::container::containers_detail::rbtree<Key, std::pair<const Key, T>, boost::container::containers_detail::select1st<std::pair<const Key, T> >, Pred, Alloc>::key_type, T>&) [with Key = std::basic_string<char, std::char_traits<char>, std::allocator<char> >, T = boost::container::map<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, int, std::less<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::pair<const std::basic_string<char, std::char_traits<char>, std::allocator<char> >, int> > >, Pred = std::less<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, Alloc = boost::interprocess::allocator<std::pair<const std::basic_string<char, std::char_traits<char>, std::allocator<char> >, boost::container::map<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, int, std::less<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::pair<const std::basic_string<char, std::char_traits<char>, std::allocator<char> >, int> > > >, boost::interprocess::segment_manager<char, boost::interprocess::rbtree_best_fit<boost::interprocess::mutex_family, boost::interprocess::offset_ptr<void>, 0ul>, boost::interprocess::iset_index> >]

插入语句的参数最终是同一类型，我该如何解决这个问题，有什么提示吗？

Answer 1

现在，您创建一个 map<string, map<string, int>> .我想您的意图只是创建一个 map<string, int> .为此，您需要对代码进行非常简单的修复:

// typedef map<std::string, int>  MappedType;
typedef int MappedType;

顺便说一句，您还可以将代码的最后一行编写为:

// m_pmap[0].insert(std::make_pair( my_string, 0) );
m_pmap[0][my_string] = 0;

更新:

看来我的直觉是错误的，而您确实想创建一个map<string, map<string, int>> , 则响应略有不同。

请注意，您的调用基本上是在尝试执行此操作:

map<string, int> x(0);
m_pmap[0][my_string] = x;

请注意，map<string, int> 没有构造函数这需要一个整数。相反，您可以执行以下任一操作:

m_pmap[0].insert(std::make_pair( my_string, map<std::string, int>()));
m_pmap[0].insert(std::make_pair( my_string, MappedType()));
m_pmap[0][my_string] = map<std::string, int>();
m_pmap[0][my_string] = MappedType();

您也可以简单地利用 map工作，并做:

m_pmap[0]["us"]["abc"] = 2030;
m_pmap[0]["us"]["def"] = 1230;