Printing lists with commas C++

Question

I know how to do this in other languages, but not C++, which I am forced to use here.

I have a Set of Strings that I\'m printing to out in a list, and they need a co

Answer 1

Because everyone has decided to do this with while loops, I'll give an example with for loops.

for (iter = keywords.begin(); iter != keywords.end(); iter++) {
  if (iter != keywords.begin()) cout << ", ";
  cout << *iter;
}

Answer 2

Something like this?

while (iter != keywords.end())
{
 out << *iter;
 iter++;
 if (iter != keywords.end()) cout << ", ";
}

Answer 3

In python we just write:

print ", ".join(keywords)

so why not:

template<class S, class V>
std::string
join(const S& sep, const V& v)
{
  std::ostringstream oss;
  if (!v.empty()) {
    typename V::const_iterator it = v.begin();
    oss << *it++;
    for (typename V::const_iterator e = v.end(); it != e; ++it)
      oss << sep << *it;
  }
  return oss.str();
}

and then just use it like:

cout << join(", ", keywords) << endl;

Unlike in the python example above where the " " is a string and the keywords has to be an iterable of strings, here in this C++ example the separator and keywords can be anything streamable, e.g.

cout << join('\n', keywords) << endl;

Answer 4

Using boost:

std::string add_str("");
const std::string sep(",");

for_each(v.begin(), v.end(), add_str += boost::lambda::ret<std::string>(boost::lambda::_1 + sep));

and you obtain a string containing the vector, comma delimited.

EDIT: to remove the last comma, just issue:

add_str = add_str.substr(0, add_str.size()-1);

Answer 5

One common approach is to print the first item prior to the loop, and loop only over the remaining items, PRE-printing a comma before each remaining item.

Alternately you should be able to create your own stream that maintains a current state of the line (before endl) and puts commas in the appropriate place.

EDIT: You can also use a middle-tested loop as suggested by T.E.D. It would be something like:

if(!keywords.empty())
{
    auto iter = keywords.begin();
    while(true)
    {
        out << *iter;
        ++iter;
        if(iter == keywords.end())
        {
            break;
        }
        else
        {
            out << ", ";
        }
    }
}

I mentioned the "print first item before loop" method first because it keeps the loop body really simple, but any of the approaches work fine.

Answer 6

to avoid placing an if inside the loop, I use this:

vector<int> keywords = {1, 2, 3, 4, 5};

if (!keywords.empty())
{
    copy(keywords.begin(), std::prev(keywords.end()), 
         std::ostream_iterator<int> (std::cout,", "));
    std::cout << keywords.back();
}

It depends on the vector type, int, but you can remove it with some helper.