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Formatting a Comma Delimated List Redux

Sun, 2009-03-08 14:14 — jason

A few weeks back, I posited the question, "What is the best way to format a comma delimited list?"

After seeing all of the succinct ways to accomplish this in other languages, I got a little jealous and decided to write this C++ algorithm which acts about the same.

I feel like there must be a c++ standard library way of doing this that I'm some how overlooking.

template <typename InItr>
std::string join(InItr begin, InItr end, const std::string &joiner)
{
  std::string ret;
 
  while (begin != end)
  {
    std::stringstream ss;
    ss << *begin;
    ret += ss.str();
    ++begin;    
    if (begin != end)
    {
      ret += joiner;
    }
  }
 
  return ret;
}

Usage:

//With an array:
int vals[] = {1,17,9};
std::cout << join(&vals[0], &vals[sizeof(vals)/sizeof(int)], ", ") << std::endl;
 
//With a vector:
std::vector<int> vec;
vec.push_back(1);
vec.push_back(17);
vec.push_back(9);
std::cout << join(vec.begin(), vec.end(), ",") << std::endl;

Comments

Sun, 2009-03-08 21:00 — cmchao (not verified)

handle last element

I prefer to erase the joiner at end

std::string ret;
std::stringstream ss;

while (begin != end) {
ss << *begin++ << joiner;
}
ret = ss.str();
ret.erase(ret.size() - joiner.size(), joiner.size());

return ret;

Sun, 2009-03-08 21:07 — cmchao (not verified)

I, embarrasedly forgot to

I, embarrasedly forgot to handle "begin == end" case ...

Mon, 2009-03-09 00:40 — Anonymous (not verified)

One way

One way more:

std::copy(vec.begin(), --vec.end(), std::ostream_iterator(std::cout, ","));
std::cout << vec.back();

Mon, 2009-03-09 18:23 — jason

Creative, but not there

Your version has two problems:

  1. List of size 0 will crash
  2. List of size 1 will have the same element twice

A corrected version would require several checks.

Sat, 2009-03-14 07:02 — Anonymous (not verified)

Another way is to use Boost's Spirit.Karma library.

Another way is to use Boost's Spirit.Karma library.

Here an example to format an container into a comma separated list:

os << karma::format(
        stream % ", ",     // format description
        c                  // data
      ) << std::endl;

Where 'c' is the container.

Have a look at the full example code at http://svn.boost.org/svn/boost/trunk/libs/spirit/example/karma/basic_fac...