c++ - 如何在 Boost 中使用元组映射？

Question

尝试将 id 映射到包含任意数据的元组:

typedef boost::tuples::tuple<std::string, std::string, unsigned char> data;
typedef std::map<uint64, data> data_map;

const data_map DATA = boost::assign::map_list_of
        (0, boost::tuples::make_tuple("XXX", "xxx", 0))
        (0, boost::tuples::make_tuple("YYY", "yyy", 1))
        (0, boost::tuples::make_tuple("ZZZ", "zzz", 2))

如何访问 DATA 映射中的元组？我正在尝试:

data_map::const_iterator itData = DATA.find(id);

然后访问它(在检查是否找到之后):

data metadata = itData->second;

抛出错误:

error: invalid initialization of reference of type 'boost::tuples::cons<const char (&)[12], boost::tuples::cons<int, boost::tuples::null_type> >::stored_head_type {aka const char (&)[12]}' from expression of type 'const char [11]'

Answer 1

吸引我的 Crystal 球:

我认为您使用过 decltype(obj)，其中 object 是 std::make_tuple("abcdefghijk",...) 或 std 的结果::领带(“abcdefghij”，...)。

这是因为错误消息谈到这种类型的元组元素 (const char (&)[12])。

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证明上面的代码没问题:

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#include <boost/assign.hpp>
#include <boost/tuple/tuple.hpp>
#include <map>

typedef boost::tuples::tuple<std::string, std::string, unsigned char> data;
typedef std::map<uint64_t, data> data_map;

int main() {

    const data_map DATA = boost::assign::map_list_of
            (0, boost::tuples::make_tuple("XXX", "xxx", 0))
            (1, boost::tuples::make_tuple("YYY", "yyy", 1))
            (2, boost::tuples::make_tuple("ZZZ", "zzz", 2));


    data_map::const_iterator itData = DATA.find(2);
    data metadata = itData->second;
}