Re: STL Vector - pass by reference?

From:

"Ben Voigt [C++ MVP]" <rbv@nospam.nospam>

Newsgroups:

microsoft.public.vc.language

Date:

Thu, 9 Aug 2007 16:05:36 -0500

Message-ID:

<esbIeks2HHA.5832@TK2MSFTNGP02.phx.gbl>

"Gerry Hickman" <gerry666uk@newsgroup.nospam> wrote in message
news:%23PFJQUs2HHA.4712@TK2MSFTNGP04.phx.gbl...

Hi,

In an earlier thread entitled "STL vector - which style of for() loop?" I
had a function that could populate a vector (with a variable number of
strings) and pass it back to the caller, but people pointed out this would
create a "copy" of the vector and it may be better to pass by reference.
Doug Harrison offered this example:

----- example start -----

I would use pass-by-reference to avoid this needless cost, e.g.

vector<string>::size_type
void GetDeviceClasses(vector<string>& guids)
{
   guids.clear();
   // If you can estimate n, reserve can eliminate reallocations.
   // guids.reserve(n);
   ...
   returns guids.size();
}

----- example end -----

but when I came to actually code this, I ran into some problems. I managed
to code something that appears to achieve the objective, but my code is
almost "back-to-front" (in terms of * and &) of what Doug posted. Can
someone clarify?

What you have looks perfectly fine. You should also either test for NULL or
else write documentation comments indicating that NULL is an illegal value.

----- my attempt -----

using namespace std; // just for this demo

vector<string> guids;
PopulateStrings(&guids);
cout << "Count of guids is now " << guids.size(); // prints 2

void PopulateStrings(vector<string> * guids)
{
   guids->clear();
   guids->push_back("test1");
   guids->push_back("test2");
}

----- end my attempt -----

--
Gerry Hickman (London UK)