Re: deque questions
jacob navia <jacob@spamsink.net> wrote:
Specifically the "swap" member. I understand what it does, but I fail to
see the utility. Why it is important to have this "swap" member? What
could be the possible uses of swapping two deque containers?
There are many practical situations where one may want to swap the
contents of two data containers. Also, swapping can often be used to
*move* all the data from one container to another (especially if the
source container is then destroyed, which will then effectively
destroy all the old data of the destination container).
The reason to have a swap() member function in STL data containers is
that's it's *way* more efficient than trying to do it in the normal way
from your own code (ie. copy the source data to a temporary data container,
then copy the destination data to the source data, and finally copy the
temporary data to the destination data). Doing it "by hand" like that would
require additional memory and would be very slow (the more the data to swap,
the slower). The swap() member functions, however, simply change some
internal pointers around, and that's it. No data is physically moved in
memory at any stage. Thus swapping usually takes just a few clock cycles
regardless of how large the data containers were.
You can imagine how this can become useful.