Re: stl skipping algorithms

From:

"Igor Tandetnik" <itandetnik@mvps.org>

Newsgroups:

microsoft.public.vc.stl

Date:

Wed, 31 May 2006 21:07:04 -0400

Message-ID:

<eqVRqhRhGHA.1612@TK2MSFTNGP04.phx.gbl>

"Super Giraffe" <muzmail@gmail.com> wrote in message
news:1149119758.831689.275270@f6g2000cwb.googlegroups.com

I have a source vector containing data, I want to copy it to a larger
vector but elements that are consecutive in the source vector should
be three elements apart in the destination vector.

Are there any copying algorithms in stl that allow me to skip elements
so a source vector:
123456...
ends up in the destination vector as
1--2--3--4--5--6--...

You can write a custom iterator adapter that skips three elements on
every increment, and use std::copy with it. It's probably more work than
it's worth. Just write a simple loop.

The following code does what I'm talking about:

for(vector<BYTE>::iterator sourcepixel= current.begin(), destpixel =
history.begin()+queue_current_length;
sourcepixel < currentcolourbmp.end();
sourcepixel++, destpixel+=queue_max_length)
*destpixel=*sourcepixel;

But it's very inefficient

What makes you think so? Why do you expect an STL algorithm to somehow
magically go faster?
--
With best wishes,
Igor Tandetnik

With sufficient thrust, pigs fly just fine. However, this is not
necessarily a good idea. It is hard to be sure where they are going to
land, and it could be dangerous sitting under them as they fly
overhead. -- RFC 1925