Re: something like Perl's join function

Seungbeom Kim <>
14 May 2006 19:42:43 -0400
Irek Szczesniak wrote:

I like the Perl's join function and want to get something similar in
C++, preferably with std or boost. In Perl you can say:

print join(", ", (10, 2, 15));

which prints "10, 2, 15".

In C++ you can get a similar thing this way:

#include <iostream>
#include <iterator>
#include <algorithm>

using namespace std;

int main()
   int table[] = {10, 2, 15};
   copy(table, table + 3, ostream_iterator<int>(cout, ", "));

However, you get "10, 2, 15, ", i.e. you get a trailing unwanted ", ".

Do you know some nifty way of getting the functionality of the Perl's
join function?

A quick implementation of mine:

#include <ostream>
#include <iterator>

template <typename T, typename CharT = char,
           typename Traits = std::char_traits<CharT> >
class ostream_join_iterator
: public std::iterator<std::output_iterator_tag, void, void, void, void>
     typedef CharT char_type;
     typedef Traits traits_type;
     typedef std::basic_ostream<CharT, Traits> ostream_type;

     ostream_join_iterator(ostream_type& s, const char_type* c = 0)
     : stream(&s), string(c), print_string(0) { }

     ostream_join_iterator& operator=(const T& value)
         if (print_string) *stream << print_string;
         print_string = string;
         *stream << value;
         return *this;

     ostream_join_iterator& operator*() { return *this; }
     ostream_join_iterator& operator++() { return *this; }
     ostream_join_iterator& operator++(int) { return *this; }

     ostream_type* stream;
     const char_type* string;
     const char_type* print_string;

Use this as a replacement of std::ostream_iterator:
std::copy(begin, end, ostream_join_iterator<int>(std::cout, ", "));

Seungbeom Kim

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