So last week I wrote about initializing a std::map from two std::vectors. How about doing the reverse? How do I get a list of the keys or a list of the values into a vector?
So I wrote a functor, based on std::unary_function, that returns the pair.first and another that returns the pair.second:

The first() template functor (from above) is used as the functor that returns the key to the std::transform() alogrithm. Here is a little fragment code that uses first(). (The test code part of a larger CPPUNIT test suite):