Re: [Boost-users] Concatenation of many std::string

From: Matt Hurd (matt.hurd_at_[hidden])
Date: 2005-02-11 14:29:45

On Thu, 10 Feb 2005 18:47:11 -0800, t. scott urban
<scottu_at_[hidden]> wrote:
> On Thu, 2005-02-10 at 18:48 +0100, Chateauneu Remi wrote:
> > I'm working on an application with many std::string concatenations,
> > everywhere. This is consuming a lot of CPU resources, due to temporary
> > strings, memory allocation, etc... Due to the size of the existing code, it
> > is not possible to make big changes.
> >
> > I tried first to transform these kind of expressions:
> > std::string a = b + c + d + e ;
> >
> > ... into ...
> >
> > std::string a(b);
> > a += c ;
> > a += d ;
> > a += e ;
> 
> It's a little ugly, but you can do
> 
> std::string a;
> a.reserve (b.size () + c.size () + d.size ());
> a += b += c += d;

That's about as fast as you can do.  If stl library authors used
expression templates you do this just as fast with a = b + c + d + e; 
See round about here
http://lists.boost.org/MailArchives/boost/msg55339.php and
http://lists.boost.org/MailArchives/boost/msg55341.php  and an
alternative though which may be better
http://lists.boost.org/MailArchives/boost/msg55413.php

Doesn't help you now though, sorry.

Matt.
matthurd_at_[hidden]