Functor for deleting objects

In a destructor for a class, I had a std::vector of pointers that I wanted to delete. I started to write the usual for(;;) loop and realized I do this often enough I should make it easy to use std::for_each().
Here’s the functor (based on std::unary_function):

template
struct deleter: public std::unary_function
{
    bool operator()(Type * ptr) const
    {
        delete ptr;
        return true;
    }
};

And here’s some sample code using it:

std::vector m_symbols;
// ...
std::for_each (m_symbols.begin(), m_symbols.end(), deleter());

I added a return of true because some other template code wasn’t happy about “return void” — supposedly something fixed in recent compilers.

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());

That new car smell

I’m closely keeping track of that cash-for-clunkers program. It sounds like the Senate is close to approving a plan that provides a $3,500 subsidy for trading in an old gas guzzler for a more efficient car!

The U.S. House of Representatives has passed a plan and the Senate is likely to do the same this week. It looks like the plan would provide a $3500 subsidy to anyone trading in a car getting less than 18 miles per gallon as long as there is at least a 4-mpg improvement. (I think I got yardage on my old car, not mileage.) A 10-mpg improvement would get you another $1000.

Copying a std::vector into a std::map

I had two vector’s with the first being the keys and the second being the values. It took a couple tries before I got the STL working for me!
The first thing was to check if the std::map constructors had something useful. It certainly seems like taking two sets of iterators would be a great way to initialize a map. No such luck.
So how about one of the std algorithms to copy the keys and values into the map? std::copy seemed likely but it only takes a single sequence. A little more digging and std::transform. The second version of std::transform takes two sequences, an output iterator, and a binary function to convert the two values from the two sequences into something that can be inserted into the output iterator. Perfect.
So how to turn the two values into a pair suitable for std::map? The std::make_pair
is exactly what is needed. The hard part is getting the syntax so you can pass it as a function: make_pair in this example.
So the code finally looks like:

#include 
#include 
#include 
#include 
#include 
#include 
void test()
{
    std::map  m;
    std::vector    keys;
    std::vector        values;
    std::transform (keys.begin(), keys.end(),
                    values.begin(),
                    std::inserter (m, m.begin()),
                    std::make_pair);
}

Closer to a new car?

It’s one step closer to happening! Getting a new car based on a trade in might actually happen. It hasn’t passed the House yet (much less the Senate) but the leadership of both parties agree on doing it.
From House Reaches a Deal on ‘Cash for Clunkers’ Program:

Under the House plan, a car trade-in that improves fuel efficiency by at least 10 miles per gallon would qualify for a $4,500 voucher, as would the trade-in of a small truck that improves efficiency by 5 miles per gallon. The new vehicle must have a minimum fuel efficiency rating of 22 miles per gallon for cars and 18 miles per gallon for small trucks.

Setting the timezone

I’ve gotten pretty careful about keeping time in UTC and then converting it to localtime for the user to understand. For the first time, I actually had to find the localtime in a non-local timezone. It’s ugly. It seems you have to mess with the TZ environment variable. Here’s what I wrote:

#include 

And here’s a code fragment that uses it:

std::string oldzone = changeTimeZone("US/Pacific");
time_t  seconds = ::time(0);
struct tm   tm_time;
localtime_r (&seconds, tm_time);
changeTimeZone(oldzone);