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

On Sat, 2005-02-12 at 06:29 +1100, Matt Hurd wrote:

On Thu, 10 Feb 2005 18:47:11 -0800, t. scott urban 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.

Yep, I borked the last line though: a += b; a += c; a+= d;

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

interesting. -- t. scott urban