How to copy vector to map in STL in a graceful way

Question

Currently, I have some data in a vector. currently, I want to transform the vector to a map.
So it will be organize as below(N is even number).

vector: element 1, element 2, element 3, element 4 ... element N.

map: key1: element 1, value1: element 2, key2: element 3 value2: element 4...

Currently, I just enumerate vector, is there any other graceful way to do it. C++11 is prefer. Thanks.

for (int x = 0; x < vec.size(); )
{
    map[vec[x]] = vec[x+1];
    x+=2;
}

Answer 1

Your code works (noting Michael J's suggestion to not process the last element if there is an odd number).

There is a small improvement that can be made. The call map[vec[x]] constructs an entry using the default constructor of the value_type, and then the copy-assignment operator copies the value from vec[x+1].

You could avoid the copy-assignment step by doing:

the_map.insert( std::make_pair(vec[x], vec[x+1]) );

I think this ends up having the map entry copy-constructed from the pair. In C++11 you can do:

the_map.emplace(vec[x], vec[x+1]);

which allows the compiler to minimize the amount of copying done. If your object supports move semantics and you want to destroy the vector afterwards, you can even go:

the_map.emplace( std::move(vec[x]), std::move(vec[x+1]) );