const std::map? | 易学教程

问题

// BOOST Includes
#include <boost/assign.hpp>             // Boost::Assign
#include <boost/assign/list_of.hpp>     // Boost::Assign::List_Of
#include <boost/assign/std/map.hpp>     // Boost::Assign::Map_List_Of
#include <boost/tuple/tuple.hpp>        // Boost::Tuples
// STD Includes
#include <map>
#include <vector>
#include <string>
// Using namespaces
using namespace std;
using namespace boost;
using namespace boost::assign;
// Consts
    const map<string, string> query_map = map_list_of<string, string>
    ("4556_SELECT_FILENAME", "SELECT FILENAME FROM Files WHERE PMU_ID = 4556")
    ("7552_SELECT_FILENAME", "SELECT FILENAME FROM Files WHERE PMU_ID = 7552")
    ("234x_SELECT_FILENAME", "SELECT FILENAME FROM Files WHERE PMU_ID = 2344 OR PMU_ID = 2345 OR PMU_ID = 2346 OR PMU_ID = 2347 OR PMU_ID = 2348")
    ("813x_SELECT_FILENAME", "SELECT FILENAME FROM Files WHERE PMU_ID = 8132 OR PMU_ID = 8133 OR PMU_ID = 8134 OR PMU_ID = 8135 OR PMU_ID = 8136");
    const map<string, std::vector<int>> vector_map = map_list_of<string, std::vector<int>>
    ("4556", list_of(4556))
    ("7552", list_of(7552))
    ("234x", list_of(2344)(2345)(2346)(2347)(2348))
    ("813x", list_of(8132)(8133)(8134)(8135)(8136));

Using boost - it's possible to init const std::containers for testing etc. making a const std::map or std::map is pretty easy as the above code shows. Creating a const map<string, std::vector<int>> is a bit more complex - but still fairly easy.

I'm trying to come up with a const std::map<boost::tuples::tuple<string, string, string>, string> but I'm failing to initialize it. Has anyone else had any luck with it ?

// Typedefs
typedef boost::tuples::tuple<string, string, string> x3_string_tuple;
// Constants
const map<x3_string_tuple, string> query_selector_map = map_list_of<x3_string_tuple, string>
("4556", "SELECT", "FILENAME"), "4556_SELECT_FILENAME"); // ETC.

回答1:

I tried this, and it fails because the keys of the map need to be comparable (with std::less, thus there needs to be an operator< defined). boost::tuple's comparison operators are defined in the header boost/tuple/tuple_comparison.hpp.

Having included that, this code works fine:

#include <boost/assign/list_of.hpp>
#include <boost/tuple/tuple.hpp>
#include <boost/tuple/tuple_comparison.hpp>
#include <map>
#include <string>

using std::string;
typedef boost::tuple<string, string, string> tpl_t;

int main() {
    using boost::assign::map_list_of;
    std::map<tpl_t, string> const m = 
        map_list_of(tpl_t("a","b","c"), "c")(tpl_t("x","y","c"), "z");
}

回答2:

I would try

const map<x3_string_tuple, string> query_selector_map = map_list_of<x3_string_tuple, string>
(x3_string_tuple("4556", "SELECT", "FILENAME"), "4556_SELECT_FILENAME");

But, honestly, maybe it's easier just to have 3 separate lists of strings, and then one-by-one combine them into a tuple and add that to a map.

来源：https://stackoverflow.com/questions/1094865/const-stdmapboosttuplestuple-stdstring

标签

c++

map

boost-tuples

const std::map<boost::tuples::tuple, std::string>?

问题

回答1:

回答2: