Nested Map Structure Create Empty Map - c++

Question

I'm don't get this to work. I want to initialize the following structure for later use.
map<pair<string,string>, map<string,vector<fs::path>>> filelist;
Thats means I provide the string pair for the first map. (e.g., "id1","id2") with an empty second map that I can fill in later. So I want to do something like this:
filelist.insert(
pair<pair<string,string>, pair<string,vector<fs::path>>>
(make_pair("id1","id2), **empty map??**));
Obviously when when I stick to the vector instead of the nested map I can do this:
filelist.insert(pair<pair<string, string>, vector<vector<fs::path>>>
(make_pair("id1","id2"),{}) );
But how can I initialize an empty map? Or is there an alternative data structure? Thanks

Answer 1

I want to initialize the following structure for later use.
map<pair<string,string>, map<string,vector<fs::path>>> filelist;
You can use operator[] to assign it.
Some thing like follows.
filelist[ std::make_pair("string1", "string2") ] = value();
where, using value = std::map< std::string, std::vector<int>>;
See live action: https://www.ideone.com/lxQir7
is there an alternative data structure?
A suggestion to reduce the complexity of your chosen data-structure is possible, only when you explain your problem and data manipulation requirements more in detail.
#include <iostream>
#include <map>
#include <string>
#include <vector>
using key = std::pair< std::string, std::string>;
using value = std::map< std::string, std::vector<int>>;
int main ()
{
std::map< key , value > filelist;
value vMap;
vMap["string"] = {1,2,3,4};
filelist[ std::make_pair("string1", "string2") ] = vMap;
// to print or access
for(auto& key_itr: filelist)
{
std::cout<< "KEY: " << key_itr.first.first << " " << key_itr.first.second << "\t VALUE: ";
for(auto& val_itr: key_itr.second)
{
std::cout << val_itr.first << " ";
for(const auto& vec: val_itr.second) std::cout << vec << " ";
}
std::cout << std::endl;
}
return 0;
}

Answer 2

You can initialize an empty map, simply by its default constructor.
It is always a better idea to name your newly introduced data types.
After all, it's a relatively complex data structure. Why don't you simplify your problem?
#include <map>
#include <vector>
#include <filesystem>
using namespace std;
using namespace std::filesystem;
using string_to_vector_of_path_map = map<string, vector<path>>;
using pair_of_strings = pair<string, string>;
using my_map = map<pair_of_strings, string_to_vector_of_path_map>;
my_map filelist;
int main()
{
filelist.insert(make_pair(make_pair("id1", "id2"), string_to_vector_of_path_map()));
return 0;
}