C++ In a Nutshell

<functional>

The <functional> header defines several functionals, or function objects. A function object is an object that has an operator( ), so it can be called using the same syntax as a function. Function objects are most often used with the standard algorithms.

For example, to copy a sequence of integers, adding a fixed amount (42) to each value, you could use the following expression:

std::transform(src.begin(  ), src.end(  ), dst.begin(  ),
               std::bind2nd(std::plus<int>(  ), 42))

The result of combining bind2nd and plus<int> is a function object that adds the value 42 when it is applied to any integer. The transform algorithm copies all the elements from src to dst, applying the functional argument to each element. See the detailed description of bind2nd and plus in this section for details.

The standard function objects are defined for C++ operators; for binding function arguments; and for adapting functions, member functions, etc., as function objects.

Boost defines functionals that extend and improve on those in the standard library. See Appendix B for information about Boost.