Pretty-print C++ STL containers

Question

Please take note of the updates at the end of this post.

Update: I have created a public project on GitHub for this library!

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Answer 1

Here is a working library, presented as a complete working program, that I just hacked together:

#include 
#include 
#include 

#include 

// Default delimiters
template  struct Delims { static const char *delim[3]; };
template  const char *Delims::delim[3]={"[", ", ", "]"};
// Special delimiters for sets.                                                                                                             
template  struct Delims< std::set > { static const char *delim[3]; };
template  const char *Delims< std::set >::delim[3]={"{", ", ", "}"};

template  struct IsContainer { enum { value = false }; };
template  struct IsContainer< std::vector > { enum { value = true }; };
template  struct IsContainer< std::set    > { enum { value = true }; };

template 
typename boost::enable_if, std::ostream&>::type
operator<<(std::ostream & o, const C & x)
{
  o << Delims::delim[0];
  for (typename C::const_iterator i = x.begin(); i != x.end(); ++i)
    {
      if (i != x.begin()) o << Delims::delim[1];
      o << *i;
    }
  o << Delims::delim[2];
  return o;
}

template  struct IsChar { enum { value = false }; };
template <> struct IsChar { enum { value = true }; };

template 
typename boost::disable_if, std::ostream&>::type
operator<<(std::ostream & o, const T (&x)[N])
{
  o << "[";
  for (int i = 0; i != N; ++i)
    {
      if (i) o << ",";
      o << x[i];
    }
  o << "]";
  return o;
}

int main()
{
  std::vector i;
  i.push_back(23);
  i.push_back(34);

  std::set j;
  j.insert("hello");
  j.insert("world");

  double k[] = { 1.1, 2.2, M_PI, -1.0/123.0 };

  std::cout << i << "\n" << j << "\n" << k << "\n";
}

It currently only works with vector and set, but can be made to work with most containers, just by expanding on the IsContainer specializations. I haven't thought much about whether this code is minimal, but I can't immediately think of anything I could strip out as redundant.

EDIT: Just for kicks, I included a version that handles arrays. I had to exclude char arrays to avoid further ambiguities; it might still get into trouble with wchar_t[].