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###Keep the const char pointers I agree with Lokis proposed changes, except that I would leave delimiter and real_delim as charT const * and change the constructor to:

infix_ostream_iterator(ostream_type &s, charT const *d = 0)
 : os(&s)
 , delimiter("")
 , real_delim(d ? d : "")
{
}

That way we reduce the cost of copying the strings, instead we just copy a pointer.

###Deduced types Mimicking the changes made to std::less in C++14, you could make operator= a template, that way we don't need to specify this type for the class. This would though break the compatibility with the std::ostream_iterator interface.

template <class T>
infix_ostream_iterator<charT, traits> &operator=(T const &item)
{
 *os << delimiter << item;
 delimiter = real_delim;
 return *this;
}

Keep the const char pointers

I agree with Lokis proposed changes, except that I would leave delimiter and real_delim as charT const * and change the constructor to:

infix_ostream_iterator(ostream_type &s, charT const *d = 0)
 : os(&s)
 , delimiter("")
 , real_delim(d ? d : "")
{
}

That way we reduce the cost of copying the strings, instead we just copy a pointer.

Deduced types

Mimicking the changes made to std::less in C++14, you could make operator= a template, that way we don't need to specify this type for the class. This would though break the compatibility with the std::ostream_iterator interface.

template <class T>
infix_ostream_iterator<charT, traits> &operator=(T const &item)
{
 *os << delimiter << item;
 delimiter = real_delim;
 return *this;
}