I'm trying to use a map within a map using the following code;
map<map <int,int>,int > multimap;
Now I want to insert the data such that multimap[1]--->(2,3), multimap[4]--->(5,6). I have been trying to insert it the following way but i guess there is a syntax error which I can't seem to figure out!
multimap.insert(pair<int,pair<int,int>(2,3)>(1));
Any help will be appreciated. And after adding, how would I display the values by using an iterator?
The map template calls for two parameters map<key, value>. The key has to have some way of comparing itself with other keys. In map it uses the < operator, so if you key with a map<int,int> you're going to have problems, since there's no defined < for an arbitrary map.
Try
map<int, map<int, int> > multimap;
multimap though... just asking for trouble.
If you want a multipmap then you need to use a multimap :) Here is declaration and an insert statement.
typedef pair<int, int> valPair;
multimap<int, valPair> mmap;
mmap.insert(make_pair(1, make_pair(2, 3)));
mmap.insert(make_pair(1, make_pair(4, 5)));
for(multimap<int, valPair>::iterator it = mmap.begin();
it != mmap.end(); ++it)
{
cout << "Key: " << it->first << " Vals:(";
<< it->second.first << ", " << it->second.second << ")" << endl;
}
It looks to me like you're confusing maps and multimaps, and keys and values.
If you want a map that maps the key '1' to the values '(2,3)' and '(4,5)' then do this:
multimap<int,pair<int,int>> myMap { {1,{2,3}}, {1,{4,5}} };
or in C++03:
multimap<int,pair<int,int> > myMap;
myMap.insert(make_pair(1,make_pair(2,3)));
myMap.insert(make_pair(1,make_pair(4,5)));
When iterating over the map each item refers to a pair where the first item of the pair is the key and the second item is the value.
for(auto &i : myMap) {
std::cout << "Key: " << i->first
<< " Value: (" << i->second.first << ',' << i->second.second << ")\n";
}
Or in C++03
for(multimap<int,pair<int,int> >::const_iterator i(myMap.begin()),end(myMap.end()); i!=end; ++i) {
std::cout << "Key: " << i->first << " Value: (" << i->second.first << ',' << i->second.second << ")\n";
}
This would print out:
Key: 1 Value: (2,3)
Key: 1 Value: (4,5)
-Firstly, there's no multimap in your code - there is simply a map called 'multimap'.
-Secondly, the structure
map< map<int, int>, int > multimap;
will not map 1-->2, 3, because you're using a map as a key, and an int as the value.
-Thirdly, the reason you're getting a build error is because the insert() method in your case takes
pair< map<int, int>, int >
What you probably want is this:
map< int, pair<int, int> > multimap;
pair<int, int> myPair( 2, 3 );
multimap.insert( pair< int, pair<int, int> >( 1, myPair ) );
map< int, pair<int, int> >::iterator iter = multimap.begin();
while( iter != multimap.end() )
{
int key = iter->first;
pair<int, int> aPair = iter->second;
++iter;
}
begin() and end() functions, and look at iterators; particularly retrieving one from begin(), incrementing it with ++, and comparing it to end().
map<int, pair<int, int>> multimapsince you want a single value that maps to a pair of values?<operator.