I need advice how to insert data into map with string and set<string>. I tried something like this, but it doesnt work:
#include <map>
#include <utility>
int main()
{
std::map<string, set<string> > mymap;
std::map<string, set<string> >::iterator it = mymap.begin();
mymap.insert ( std::pair<string, set<string> > ("car" , "orange") );
return (0);
}
Could someone help me? Thank you in advance.
I don't know why it seems so popular these days to avoid operator[] for maps, it's so much more elegant than insert. Unless of course, the slight differences (such as the need for a default constructor) cause it to not work for you, or you've determined that it is causing a performance problem. For your purposes, as you've described them, it should work fine.
mymap["car"].insert("orange");
This will construct the set if it doesn't already exist, and it will insert an element into it. In comments, you've expressed a desire to add further elements to the set, and you can use the exact same syntax.
mymap["car"].insert("blue");
If you want to ensure you have a fresh, empty set before inserting, you can always call clear() on it.
auto & car_set = mymap["car"];
car_set.clear();
car_set.insert("orange");
insert instead of operator [] , how can it be done if the key is already present in the map?Two methods:
set<string> myset;
myset.insert("orange");
//first method
mymap["car"] = myset; //will overwrite existing data!!
//second method
mymap.insert(make_pair("car", myset));
#include <map>
#include <set>
#include <string>
int main() {
std::map< std::string, std::set< std::string> > mymap;
std::set< std::string> s;
s.insert( "orange");
mymap.insert( std::make_pair( std::string("car") , s));
return 0;
}
To add new element to existing std::set:
//add string to set identified by key "car"
if ( mymap.find( "car") != mymap.end()) {
std::set< std::string>& s_ref = mymap[ "car"];
s_ref.insert( "blue");
}
Please check this online example.
#include <map>
#include <set>
#include <string>
#include <iostream>
using namespace std;
void insertValue(map<string, set<string> >& myMap,
string const& key,
string const& value)
{
// Check whether there is already a set given the key.
// If so, insert to the existing set.
// Otherwise, create a set and add it to the map.
map<string, set<string> >::iterator found = myMap.find(key);
if ( found != myMap.end() )
{
cout << "Adding '" << value << "' to an existing set of " << key << "s.\n";
found->second.insert(value);
}
else
{
cout << "Adding '" << value << "' to a new set of " << key << "s.\n";
set<string> temp;
temp.insert(value);
myMap.insert(make_pair(key, temp));
}
}
int main()
{
map<string, set<string> > mymap;
insertValue(mymap, "car", "orange");
insertValue(mymap, "car", "blue");
insertValue(mymap, "car", "red");
insertValue(mymap, "truck", "orange");
insertValue(mymap, "truck", "blue");
return 0;
}
insertValue function achieves the exact same thing as simply doing: mymap[key].insert(value);
mymap[key] = value;? Otherwise looks like the second part of yourpairis not aset.mymap.insert({"car", {"orange"}});should work. The problem with the code in the question is that "orange" is not a set.