Re: Array vs Vector performance

From:

Alberto Ganesh Barbati <AlbertoBarbati@libero.it>

Newsgroups:

comp.lang.c++.moderated

Date:

Mon, 21 Jul 2008 15:17:18 CST

Message-ID:

<2d0hk.31008$Ca.15717@twister2.libero.it>

krisprad@yahoo.co.uk ha scritto:

There appears to be significant performance difference between the
array and the vector.

The helper functions measure usage excluding any allocation related
timing.
However, cout statements are also instrumented to simulate observable
behaviour, but they seem unlikely to account for this variation.

One explanation I could think of is, vector, being allocated
elsewhere
is losing out on cache hits, causing more page faults.

Is this difference expected or am I missing something?

These numbers are very suspicious. I don't expect to see any significant
difference between the two. Actually, I expect to see no difference at
all with a reasonably optimizing compiler. Are you sure you are not
doing your benchmark with some "debug feature" enabled? For example in
VC++ 8.0 all accesses to std::vector are checked for invalid indexes
even in release builds, unless you define the macro _SECURE_SCL to the
value 0. See

   http://msdn.microsoft.com/en-us/library/aa985965(VS.80).aspx

for reference.

HTH,

Ganesh

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