Re: optimizing std::map or std::hash_map for speed

From:

"Carl Daniel [VC++ MVP]" <cpdaniel_remove_this_and_nospam@mvps.org.nospam>

Newsgroups:

microsoft.public.vc.stl

Date:

Fri, 1 Sep 2006 19:03:31 -0700

Message-ID:

<OCoS#PjzGHA.2196@TK2MSFTNGP03.phx.gbl>

Costellj@gmail.com wrote:

Hello,

I am converting an app written in mfc to be cross platform. The goal
is for the app to be as fast or faster than it's mfc's equivalent. I
am doing some preliminary tests with std::map and std::hash_map
compared with CMap. I believe I am missing something in how I am
implementing the stl containers, or perhaps my test is bad. In
general this is my test:

get current time
for Cmap I call InitHash() with a prime number bigger than what I need
for std::map, std::hash_map I use the get allocater to allocate the
space I need in advance
then I call a for loop and insert 2 million values
I then subtract the current time from the previous to get how many
seconds it takes

In my Cmap code this take between 8 and 9 seconds, but with each of
the stl it is well over 30 seconds.

I know that there must be an error in something I'm doing to get this
drastic of differences. I just can't figure it out for the life of me

First, there's no such thing as std::hash_map, although some standard
library implementations include one. Exactly what compiler/library are you
using?

Second, please show some code - both the MFC version and the STL version -
so that we can see what you're doing.

Third, please include the compiler command-line options (or project
configuration) that you're using. There's a big difference, especially in
VC7.1 and later, between debug and release builds (much bigger for STL than
for MFC).

-cd