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By far the simplest is to define a global "less than" operator for your struct in stead of as a member function. std::map uses - by default - the 'lessthan' functor which, in turn, uses the global "operator<" defined for the key type of the map.
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!
List: A list in STL is used to implement the doubly-linked lists. Unlike an array, lists are used to store the data, which is not contiguous.
A map is a data structure that stores information in the form of key and value pairs. In C++, map is defined in STL (standard template library) and store keys in an ordered form. map<key_type , value_type> map_name; The data type of any of these two data of the map can be any of the data types.
I have the following code:
struct Node
{
int a;
int b;
};
Node node;
node.a = 2;
node.b = 3;
map<int, int> aa;
aa[1]=1; // OK.
map<Node, int> bb;
bb[node]=1; // Compile error.
When I tried to map an instance of my struct Node to an int, I got a compile error. Why?
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