back_insert_iterator with remove_copy_if

Question

I am trying to use a back_insert_iterator with remove_copy_if using vectors but I have compile errors.

Do you know why the code below is wrong?

#include <iostream>
#include <string>
#include <algorithm>
#include <cassert>
#include <vector>
#include <iterator>
#include <functional>

struct checkRem : std::unary_function<int,bool> {
    int _val;
    checkRem( int val ): _val(val){}
    bool operator()(int aVal){ return aVal > _val;}
};

int main( int argc, char** argv )
{
int _vIn[] = {1,2,3,4,2,3,4,3,6,7};
std::vector< int > vIn( _vIn, _vIn + (sizeof( _vIn )/sizeof(_vIn[0])));

// remove with copy
std::vector<int>vOut;
std::back_insert_iterator< std::vector<int> >  bit( vOut );

std::vector< int >::iterator new_end = 
std::remove_copy_if(
    vIn.begin(),
    vIn.end(),
    bit,
    checkRem(2)
);
}
back_insrt_iter.cpp: In function ‘int main(int, char**)’:
back_insrt_iter.cpp:30: error: conversion from      
‘std::back_insert_iterator<std::vector<int, std::allocator<int> > >’ to non-scalar  
type ‘__gnu_cxx::__normal_iterator<int*, std::vector<int, std::allocator<int> > >’ 
requested

Answer 1

std::remove_copy_if() returns an iterator of the same type as the output iterator. In this case, it's a std::back_inserter_iterator. You're not changing the input container, but you're copying into an output container the elements for which the predicate doesn't hold.

In short, use std::remove_if() if you want to change your input container.