Technology

A better output_iterator

I was using the std::stream_iterator, for example:

    std::vector    vals;
    vals.push_back (12);
    vals.push_back (22);
    vals.push_back (5);
    vals.push_back (30);
    // The std::ostream_iterator appends the ","
    std::ostringstream  str3;
    std::copy (vals.begin(), vals.end(), std::ostream_iterator (str3, ","));
    CPPUNIT_ASSERT_EQUAL (std::string ("12,22,5,30,"), str3.str());

It has the “,” after the last item.
So here’s an implementation that doesn’t append the seperator after the last one:

#ifndef INCLUDED_OUTITER_H
#define INCLUDED_OUTITER_H
#include 
/**
 * A replacement for std::ostream_iterator that doesn't put the
 * seperator after the last item.
 */
template<typename Type, typename CharType = char,
     typename Traits = std::char_traits >
class outiter : public std::iterator
{
public:
    typedef CharType            char_type;
    typedef Traits          traits_type;
    typedef std::basic_ostream    ostream_type;
    /// Initialize from a stream
    outiter (ostream_type &stream)
    : m_stream (&stream),
      m_string (0),
      m_started (false)
    {}
    /// Copy constructor
    outiter (const outiter &copy)
    : m_stream (copy.m_stream),
      m_string (copy.m_string),
      m_started (copy.m_started)
    {}
    /// Initialize from a stream and the seperator
    outiter (ostream_type &stream, const CharType *str)
    : m_stream (&stream),
      m_string (str),
      m_started (false)
    {}
    /// Assignment actually does the output
    outiter &
    operator=(const Type &value)
    {
    if (!m_started)
    {
        m_started = true;
    }
    else if (m_string)
    {
            (*m_stream) << m_string;
    }
    (*m_stream) << value;
    return *this;
    }
    /// Just return a reference to this
    outiter &
    operator*()
    {
    return *this;
    }
    /// Just return a reference to this
    outiter &
    operator++()
    {
    return *this;
    }
    /// Just return a reference to this
    outiter &
    operator++(int)
    {
    return *this;
    }
private:
    /// The stream to write to
    ostream_type *      m_stream;
    /// The seperator (may be NULL)
    const char_type *       m_string;
    /// Flag to indicate if we've output anything
    bool            m_started;
};
#endif /* INCLUDED_OUTITER_H */

And here’s the corresponding code to use it:

    std::ostringstream  str;
    std::copy (vals.begin(), vals.end(), outiter (str, ","));
    CPPUNIT_ASSERT_EQUAL (std::string ("12,22,5,30"), str.str());
Standard

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