将指针映射转换为对象映射

Question

I have a map which has pointers to objects as keys (values are int). Given this, I want to create a map that is identical to the original map, but I want the keys to be the corresponding objects (aka dereferenced keys)

Here is my code:

map<const Point*, int> m1 = createMap();
map<Point,int> temp;
for_each(q.begin(), q.end(), [&temp](pair<const Point*, int> p){temp.insert(make_pair(*(p.first),p.second));});

What I'm trying to do is call a lambda that simpley derefrences the keys of the initial map.

The compiler however complains that "/usr/include/c++/4.8/bits/stl_function.h|235|error: no match for 'operator<' (operand types are 'const Point' and 'const Point')|"

Am I making a foolish mistake somewhere?

Answer 1

You have to define operator< for your class Point.

A map is an ordered collection of elements. Hence you need to implement a function to order them. By default, that function is operator< , but you can specify a different one in the constructor if you want.

Se here, for example:

http://www.cplusplus.com/reference/map/map/