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Based on a previous question, I am trying to create a map using a pair of integers as a key i.e. map<pair<int, int>, int> and I've found information on how to insert:
#include <iostream> #include <map> using namespace std; int main () { map<pair<int, int>, int> mymap; mymap.insert(make_pair(make_pair(1,2), 3)); //edited } but I can't seem to access the element! I've tried cout << mymap[(1,2)] << endl; but it shows an error, and I can't find information on how to access the element using the key. Am I doing something wrong?
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Do you mean cout << mymap[make_pair(1,2)] << endl; ? (1,2) is non-sensical, at least in this context. You must have an std::pair to be used as your key, and that means following what @andre just commented. Yes!
Using default order So, C++ expects operator< to be defined for the type used for map's keys. Since the operator< is already defined for pairs, we can initialize a std::map with std::pair as the key.
int a=10,b=20; map < pair < int,int >, int > m; pair < int,int >numbers = make_pair(a,b); int sum=a+b; m[numbers]=sum; Our map will have its key as pairs of numbers. We can access the integer values of pair variable using dot(.) operator.
A pair is a single unit with two members. A map has keys and values in it. So you can use pairs to fill up a map, the elements of the pair becoming key and value.
you need a pair as a key cout << mymap[make_pair(1,2)] << endl; What you currently have cout << mymap[(1,2)] << endl; is not the correct syntax.
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mymap[make_pair(1,2)]
or, with compiler support:
mymap[{1,2}]
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