use stable_partition on the vecCopy - maintains relative order : partition « STL Algorithms Modifying sequence operations « C++ Tutorial

1. C++ Tutorial
2. STL Algorithms Modifying sequence operations
3. partition

#include <algorithm>
#include <vector>
#include <iostream>
using namespace std;
bool IsEven (const int& nNumber)
{
    return ((nNumber % 2) == 0);
}

int main ()
{
    vector <int> v;

    for (int nNum = 0; nNum < 10; ++ nNum)
        v.push_back (nNum);

    // a copy of the sample vector
    vector <int> vecCopy (v);

    // use stable_partition on the vecCopy - maintains relative order
    stable_partition (vecCopy.begin (), vecCopy.end (), IsEven);

    for (size_t nItem = 0; nItem < vecCopy.size (); ++ nItem)
        cout << vecCopy [nItem] << ' ';

    return 0;
}