C++ In a Nutshell

Name

ptr_fun function template — Creates a pointer to a function object

Synopsis

template <typename Arg1, typename Arg2, typename Rtn>
  pointer_to_binary_function<Arg1,Arg2,Rtn>
    ptr_fun(Rtn (*f)(Arg1, Arg2));
template <typename Arg, typename Rtn>
  pointer_to_unary_function<Arg, Rtn>
    ptr_fun(Rtn (*f)(Arg));

The ptr_fun function template creates a function object from a pointer to a function. The resulting function object has an operator( ) that calls the function. Functions of one and two arguments are supported.

For example, suppose you have two numeric vectors, a and b, and you want to raise each element of a to the power of the corresponding element in b, saving the result in a third vector, c. There is no predefined power function object, so you can use ptr_fun and your own power function instead, as shown in Example 13-13.

Example

Example 13-13. Wrapping the pow function in a function object

std::vector<double> a, b, c;
double power(double x, double y)
{
  return std::pow(x, y);
}
...
std::transform(a.begin(), a.end(  ), b.begin(  ), c.begin(  ),std::ptr_fun(power));

See Also

mem_fun function template, mem_fun_ref function template, pointer_to_binary_function class template, pointer_to_unary_function class template