std::unary_function is an empty class that serves as the base class of a unary functor. A unary functor defines operator(), where operator() takes one argument. The advantage of using std::unary_function is its many typedefs, so that the derived functors fit in more algorithms.

Example: MakeAbs


#include <algorithm>

#include <cmath>

#include <functional>

#include <vector>



template <class T> struct Abs : public std::unary_function<T,T>

{

  const T operator()(const T& x) const { return std::abs(x); }

};



void MakeAbs(std::vector<int>& v)

{

  std::transform(v.begin(),v.end(),v.begin(),Abs<int>());

}

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(C++) std::unary_function

Example: MakeAbs