Slicing a vector

Taken from here:

std::vector<myvector::value_type>(myvector.begin()+start, myvector.begin()+end).swap(myvector);

Usage example:

#include <iostream>
#include <vector>

int main ()
{
    std::vector<int> indexes{3, 6, 9};

    for( auto index : indexes )
    {
        int slice = 3;
        std::vector<int> bar{1, 2, 3, 4, 5, 6, 7, 8, 9};
        std::vector<int>( bar.begin() + index - slice, bar.begin() + index ).swap(bar);

        std::cout << "bar index " << index << " contains:";
        for (unsigned i=0; i<bar.size(); i++)
            std::cout << ' ' << bar[i];
        std::cout << '\n';
    }

    return 0;
}

Outputs:

bar index 3 contains: 1 2 3
bar index 6 contains: 4 5 6
bar index 9 contains: 7 8 9

I learnt Python before I learnt C++. I wondered if C++ offered slicing of vectors like slicing in Python lists. Took a couple of minutes to write this function that allows you to slice a vector analogous to the way its done in Python.

vector<int> slice(const vector<int>& v, int start=0, int end=-1) {
    int oldlen = v.size();
    int newlen;

    if (end == -1 or end >= oldlen){
        newlen = oldlen-start;
    } else {
        newlen = end-start;
    }

    vector<int> nv(newlen);

    for (int i=0; i<newlen; i++) {
        nv[i] = v[start+i];
    }
    return nv;
}

Usage:

vector<int> newvector = slice(vector_variable, start_index, end_index);

The start_index element will be included in the slice, whereas the end_index will not be included.

Example:

For a vector v1 like {1,3,5,7,9}

slice(v1,2,4) returns {5,7}

You'd just use a pair of iterators:

typedef std::vector<int>::iterator vec_iter;

void doSomething(vec_iter first, vec_iter last) {
    for (vec_iter cur = first; cur != last; ++cur) {
       std::cout << *cur << endl;
    }
}

int main() {
   std::vector v();
   for (int i= 0; i < 10; ++i) { v.push_back(i); }

   doSomething(v.begin() + 1, v.begin() + 5);
   doSomething(v.begin() + 2, v.begin() + 4);
   return 0;
}

Alternatively, the Boost.Range library should allow you to represent iterator pairs as a single object, but the above is the canonical way to do it.