c++ std Copying a list to map

Question

Consider the following:

struct A
{
    int i;
    double d;
    std::string s;
};

std::list<A> list_A; 

I'd like to copy all the elements of list_A to a map such that every pair in the map will consist of an element from list_A as value and its string s as key. Is there a way of doing it that is more elegant than looping through the list and insert each element along with its string as key to the map?

Answer 1

This should get you the idea of how to use transform:

std::pair<std::string, A> pairify(const A& a) { return std::make_pair(a.s, a); }

std::transform(list.begin(), list.end(), std::inserter(map, map.end()), pairify);

The reason to use the inserter is:

An insert interator is a special type of output iterator designed to allow algorithms that usually overwrite elements (such as copy) to instead insert new elements automatically at a specific position in the container.

Answer 2

I love standard library algorithms and lambdas but it doesn't get much simpler than:

for (const A& value : list_A) {
    map_A.insert(std::make_pair(value.s, value));
}

The other methods are doing the equivalent of this code and this loop is readable and just as fast.