Using an unordered_map of unordered_sets

Question

If I have an unordered map of unordered_sets indexed by strings, such as

static boost::unordered_map<std::string, boost::unordered_set<std::string> > UseMap;

I had a couple question about using this data structure. Is there anyway for me to insert a new value into the set indexed in the map without having to use a pointer to the set or reindex the map value?

Second question, I'm getting an unresolved external symbol error when I try to index into the map. As an example,

void AddUse(const std::string &character, const std::string& used)
{
    auto set = UseMap[character];
    set.insert(used);
    UseMap[character] = set;

}

I'm not sure why this is causing an unresolved symbol error, so any guidance there would be helpful.

Thanks in advance

EDIT: Any use of UseMap[character] causes the unresolved symbol error

Also added error code and source example

Full Class

#pragma once
#ifndef _SINGLEUSE_H_
#define _SINGLEUSE_H_
#include <boost/unordered_map.hpp>
#include <boost/unordered_set.hpp>
#include <string>
#include <vector>
class SingleUse
{
public:
    void AddUse(const std::string& character, const std::string& used)
    {
        UseMap[character].insert(used);
    }

    bool HasUsed(const std::string &character, const std::string& used)
    {
        return false;//UseMap[character].find(used) != UseMap[character].end();
    }

    void ClearAll()
    {
        UseMap.clear();
    }
private:
    static boost::unordered_map<std::string, boost::unordered_set<std::string> > UseMap;
};

And the full error message:

Error 52 error LNK2001: unresolved external symbol "private: static class boost::unordered_map,class std::allocator >,class boost::unordered_set,class std::allocator >,struct boost::hash,class std::allocator > >,struct std::equal_to,class std::allocator > >,class std::allocator,class std::allocator > > >,struct boost::hash,class std::allocator > >,struct std::equal_to,class std::allocator > >,class std::allocator,class std::allocator > const ,class boost::unordered_set,class std::allocator >,struct boost::hash,class std::allocator > >,struct std::equal_to,class std::allocator > >,class std::allocator,class std::allocator > > > > > > SingleUse::UseMap" (?UseMap@SingleUse@@0V?$unordered_map@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@V?$unordered_set@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@U?$hash@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@boost@@U?$equal_to@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@2@V?$allocator@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@2@@boost@@U?$hash@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@4@U?$equal_to@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@2@V?$allocator@U?$pair@$$CBV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@V?$unordered_set@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@U?$hash@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@boost@@U?$equal_to@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@2@V?$allocator@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@2@@boost@@@std@@@2@@boost@@A) G:\Documents\Programming Projects\KHMP\KHMP_Repo\KHMP\build\KHMP\KHMP\KHMPMain.obj

Answer 1

First question, yes, it should be fine as long as you assign the result to a reference.

Do this:

boost::unordered_set<std::string>& set = UseMap[character];

Now set is a reference to a value in the map. (I'm not sure what auto gives you, so I put the type in full; you may be able to get away with using auto.) Any changes you make to set will be reflected in the map.

set.insert(used); // This updates the map, no need to write it back in.

Answer 2

Ok, the unresolved symbol is because I don't instantiate the static variable anywhere. I forgot you had to do that in C++, my mistake. Thanks for the help with the sets