C++ iterator, Func as operator () or std:function and predicate as func

(1) there are various kinds of iterators: forward, random, input, output,bi-directional, iterator_traits::iterator_category
(2) for(; ...) will avoid post increment iterator, since some does not support iter++
(3) C++ func are struct with operator() overridden or std::function as a function_ptr
(4) iterator can be de-referenced or indexed in *, []

#include "stdafx.h"
#include <iostream>
#include <string>
#include <vector>
#include <functional>
#include <algorithm>

using namespace std;

template<typename ForwardIter, typename Func>
void adjacent_pair(ForwardIter first, ForwardIter last, Func func)
{
 if (first != last)
 {
  ForwardIter trailer = first;
  ++first;
  for (; first != last; ++first, ++trailer)
   func(*trailer, *first); 
 }
};

template<typename SourceIter, typename TargetIter, typename Predicate>
std::pair<SourceIter, TargetIter> copy_while(SourceIter srcFirst, SourceIter srcLast, TargetIter tgt, Predicate p)
{
 for (; srcFirst != srcLast && p(*srcFirst); ++srcFirst,++tgt )
  *tgt = *srcFirst;
 return std::make_pair(srcFirst,tgt);
};

struct func_cout
{
 inline void operator() (int a, int b) const { cout << a << " " << b << endl; }
};

struct func_predicate_even
{
 inline bool operator() (int a) const { return a % 2==0; }
} 

inline void print(int a,int b) { cout << a << "|" << b << endl;}

int main()
{
 vector<int> v = { 2,16,36,109,8,999,90,5 };

 func_cout a_func;
 adjacent_pair<vector<int>::iterator, func_cout>(v.begin(), v.end(),a_func);
 std::function<void(int,int)> f_ptr = print;
 adjacent_pair<vector<int>::iterator, std::function<void(int, int)>>(v.begin(), v.end(), f_ptr);

 vector<int> w(5);
 func_predicate_even pred;
 auto ret_iter = copy_while(v.begin(),v.end(), w.begin(),pred);
 cout << *ret_iter.first <<"**"<< *ret_iter.second <<"copied "<<w[1]<< endl;

 std::string s;
 getline(cin, s);
    return 0;
}