How to deal with last comma, when making comma sep

Question

Possible Duplicates:
Don't print space after last number
Printing lists with commas C++

#include <vector>
#include <iostream>
#include <sstream>
#include <boost/foreach.hpp>
using namespace std;

int main()
{
   vector<int> VecInts;

   VecInts.push_back(1);
   VecInts.push_back(2);
   VecInts.push_back(3);
   VecInts.push_back(4);
   VecInts.push_back(5);

   stringstream ss;
   BOOST_FOREACH(int i, VecInts)
   {
      ss << i << ",";
   }

   cout << ss.str();

   return 0;
}

This prints out: 1,2,3,4,5, However I want: 1,2,3,4,5

How can I achieve that in an elegant way?

I see there is some confusion about what I mean with "elegant": E.g. no slowing down "if-clause" in my loop. Imagine 100.000 entries in the vector! If that is all you have to offer, I'd rather remove the last comma after I have gone through the loop.

Answer 1

You can either trim the string at the end, or using single for loop instead of foreach and dont concatenate at the last iteration

Answer 2

I like moving the test outside the loop.
It only needs to be done once. So do it first.

Like this:

if (!VecInts.empty())
{
    ss << VecInts[0]

    for(any loop = ++(VecInts.begin()); loop != VecInts.end(); ++loop)
    {
        ss << "," << *loop;
    }
}

Answer 3

Detecting the one before last is always tricky, detecting the first is very easy.

bool first = true;
stringstream ss;
BOOST_FOREACH(int i, VecInts)
{
  if (!first) { ss << ","; }
  first = false;
  ss << i;
}

Answer 4

This would work

stringstream ss;
BOOST_FOREACH(int const& i, VecInts)
{
   if(&i != &VecInts[0])
     ss << ", ";
   ss << i;
}

I suspect with "elegant" you mean "without introducing a new variable". But I think I would just do it "non-elegant" if I couldn't find anything else. It's still clear

stringstream ss;
bool comma = false;
BOOST_FOREACH(int i, VecInts)
{
   if(comma)
     ss << ", ";
   ss << i;
   comma = true;
}

Imagine 100.000 entries in the vector! If that is all you have to offer, I'd rather remove the last comma after I have gone thorough the loop.

You are saying that as if printing ss << i is one machine instruction. Come on, executing that expression will execute lots of if's and loops inside. Your if will be nothing compared to that.