Re: Efficient insertion in a std::multimap

From:

Barry <magnus.moraberg@gmail.com>

Newsgroups:

comp.lang.c++

Date:

Sat, 22 Aug 2009 14:16:08 -0700 (PDT)

Message-ID:

<29b70ea7-1959-4b82-adef-1ad46672fe6b@a13g2000yqc.googlegroups.com>

On 22 Aug, 23:02, Barry <magnus.morab...@gmail.com> wrote:

On 22 Aug, 20:43, Sam <s...@email-scan.com> wrote:

Barry writes:

Hi,

Hope this doesn't get lost beneath all the spam.

I have the following container which I wish to create and store
objects of type MyObject in-

class Phase : public std::multimap<double, MyObject>
{
public:
   Phase();
};

Phase::Phase()
{
   MyObject myObject;
   std::pair<double,Note> pair(0.0,myObject);
   insert (pair);
}

A lot of copy constructors are being called for MyObject which I'd
like to avoid. But first, I'm not understanding what is happening for
the line: insert (pair);. Here, the copy constructor is called twice
and the default destructor once which suggests to me that a temp
object is create, but why?

"std::pair<double,Note> pair(0.0,myObject)" is the first copy construct=

or.

The second copy constructor occurs in the insert() method.

Finally, is t=

here a way to cut down on all

the copies?

Store pointers, instead of the actual objects. Of course, that creates =

whole bunch of other issues.

application_pgp-signature_part
< 1KVisaH=E4mta

Thanks for the reply. How might I use pointers to do this since I wish
to store many MyObject objects within a Phase Object? If I were to use
pointers, then I would do something like this -

Phase::Phase()
{
  MyObject* myObject = new MyObject();
  std::pair<double,Note*> pair(0.0,myObject);
  insert (pair);

}

But I will be storing a whole bunch of MyObject objects within a Phase
object, so I'm still going to need to keep track of them in order to
delete them in Phase's destructor. But how would I keep track of them?

Thanks again,

Barry

I could have a for loop in the destructor for Phase which loops
through all the elements, deleting them. Does this sound reasonable?