How do I find an element position in std::vector?

Question

I need to find an element position in an std::vector to use it for referencing an element in another vector:

int find( const vector& whe         


        

Answer 1

Something like this, I think. find_if_counted.hpp:

#ifndef FIND_IF_COUNTED_HPP
#define FIND_IF_COUNTED_HPP

#include 

namespace find_if_counted_impl
{
    template 
    struct func_counter
    {
        explicit func_counter(Func& func, unsigned &count) :
        _func(func),
        _count(count)
        {
        }

        template 
        bool operator()(const T& t)
        {
            ++_count;

            return _func(t);
        }

    private:
        Func& _func;
        unsigned& _count;
    };
}

// generic find_if_counted,
// returns the index of the found element, otherwise returns find_if_not_found
const size_t find_if_not_found = static_cast(-1);

template 
size_t find_if_counted(InputIterator start, InputIterator finish, Func func)
{
    unsigned count = 0;
    find_if_counted_impl::func_counter f(func, count);

    InputIterator result = find_if(start, finish, f);

    if (result == finish)
    {
        return find_if_not_found;
    }
    else
    {
        return count - 1;
    }
}

#endif

Example:

#include "find_if_counted.hpp"
#include 
#include 
#include 

typedef std::vector container;

int rand_number(void)
{
    return rand()  % 20;
}

bool is_even(int i)
{
    return i % 2 == 0;
}

int main(void)
{
    container vec1(10);
    container vec2(10);

    std::generate(vec1.begin(), vec1.end(), rand_number);
    std::generate(vec2.begin(), vec2.end(), rand_number);

    unsigned index = find_if_counted(vec1.begin(), vec1.end(), is_even);

    if (index == find_if_not_found)
    {
        std::cout << "vec1 has no even numbers." << std::endl;
    }
    else
    {
        std::cout << "vec1 had an even number at index: " << index <<
            " vec2's corresponding number is: " << vec2[index] << std::endl;
    }
}

Though I feel like I'm doing something silly... :X Any corrections are welcome, of course.