Is there a simple / elegant way to push a Range of integers to an STD vector?

Question

I have a simple task which is to initialize an std::vector<int> with a range of integers.

The range is given by the user, and i try to avoid using a for loop.

Something like:

void addRange(std::vector<int>& vReturn, int nStart, int nEnd)
{
    vReturn.clear();

    // straightforward solution
    for (int nInteger = nStart; nInteger <= nEnd; nInteger++)
    {
         vReturn.push_back(nInteger);
    }
    //////////////////////////////////////////////

    // Elegent Pseudo-Code
    vReturn.add_range(nStart, nEnd);   // <<- is this doable?

}

since you use C++11, why not `std::vector addRange(int nStart, int nEnd)` as signature and return the vector by-value? Furthermore, why the `const` for your function parameters? — TemplateRex, May 28 '14 at 13:26
@TemplateRex - the `const` are redundant, just a habbit of mine to define any `[in]` parameter as `const` although passed by value... this makes the interface much more clear with what is `[in]` and what is `[out]` — NirMH, May 28 '14 at 20:31

ForEveR · Accepted Answer · 2014-05-28T10:52:55.113

9

You can do this in C++11, using algorithm iota.

vReturn.clear();
vReturn.resize((nEnd - nStart) + 1);
std::iota(vReturn.begin(), vReturn.end(), nStart);

You can also use boost::irange.

auto range = boost::irange<int>(nStart, nEnd + 1);
vReturn.assign(range.begin(), range.end());

edited May 28 '14 at 10:52

answered May 28 '14 at 10:45

ForEveR

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what about using std::copy? – WileTheCoyot May 28 '14 at 11:06
@WileTheCoyot where? Why not use assign? – ForEveR May 28 '14 at 11:09
what are the differences betwen std::copy and std::iota? – WileTheCoyot May 28 '14 at 12:04
@WileTheCoyot please look at link, that is in post. copy just copy. iota fill the range with incremented values. – ForEveR May 28 '14 at 12:12

score 0 · Answer 2 · answered May 28 '14 at 12:23

I have an alternative solution and it does not use for loop and does not use boost or C++11

#include <iostream>
#include <vector>

using namespace std;

struct Add{

  void operator()(int x, int y, vector<int>& vec)
  {
    if(x > y)
      return;

    vec.push_back(x);
    operator()(++x, y, vec);
  }
};

void addRange(std::vector<int>& vReturn, const int nStart, const int nEnd)
{
   vReturn.resize(nEnd - nStart); 
   vReturn.clear(); 
   Add()(nStart, nEnd, vReturn);  //update the vector using Functor object
}

int main()
{
   vector<int> vec;
   int start = 1, end = 10;

   addRange(vec, start , end);


   return 0;
}

Is there a simple / elegant way to push a Range of integers to an STD vector?

2 Answers2