Most useful or amazing STL short liners

Question

I\'m looking for practical and educational samples of C++ / STL code fitting in few lines. My actual favorites are:

1. Empty a vector freeing its reserved memory:<

Answer 1

Using std::for_each in combination with a lambda function (since C++11)

std::vector v(20);

std::for_each( v.begin(), v.end(), [] (int item)
{
    std::cout << item;
} );

instead of

for(std::vector::const_iterator it = v.begin(); it != v.end(); ++it)
{
    std::cout << *it;
}

makes for better looking loops.