Re: [boost] Re: std::complex design (Was: N-Dimensional array lib rary submission...)

From: David Abrahams (david.abrahams_at_[hidden])
Date: 2002-03-06 16:44:27

----- Original Message -----
From: "Stewart, Robert" <stewart_at_[hidden]>

> The memory for the vector is not reallocated, and the elements are not
> copied from the old to a new allocation.  That is, with a judicious
call to
> reserve() before push_back(), size() < capacity() will always be true,
so x
> will be copied into the uninitialized memory at end() and the size
will be
> incremented.  Thus, there is no memory/copy performance penalty which
is
> what I thought "slow" was meant to imply.  If a comparison of two
integers
> and the increment of another is more overhead than you can bear --
though it
> certainly doesn't justify the label "slow"! -- then you need a
fixed-size
> array such as a C array or a wrapper class of a C array.
>

You don't /need/ plain C arrays to avoid the checks for each element;
that's what insert(pos, start, finish) and resize(n, x) are for.

On huge vectors of complex<>, even the member initializations in the
complex<> constructor are too expensive, however.

-Dave