rare occasion where I really want a post decrement (like in a subscript).
read. I guess I have a lot of faith in the optimizer :o)
On Wed, 13 Feb 2008 12:12:53 -0500, Joseph M. Newcomer
<newcomer@flounder.com> wrote:
But the real question is not "does it have an extra line of C code in the
function?" but
"does it generate any more code?" The ultimate test is by looking at the
generated
machine code. If I weren't going to spend the entire afternoon in
tax-mode, I try a few
tests to see what the real costs were for a set of STL iterators.
joe
At best, you will come up with an answer that applies to one compiler, one
set of compiler settings, and whatever classes you test. See my reply to
Giovanni for more reasons why this won't be the basis for any general
advice. Specifically, it matters if the compiler has the class definition
(or the functions are inline), which it will for STL classes, because
they're templates. If you do perform the test you described, be sure to
compare and contrast it with:
struct X
{
X& operator++();
X operator++(int);
};
void f1(X& x)
{
++x;
}
void f2(X& x)
{
x++;
}
*****
The C++ FAQ says:
[13.15] Which is more efficient: i++ or ++i?
http://www.parashift.com/c++-faq-lite/operator-overloading.html#faq-13.15
<q>
++i is sometimes faster than, and is never slower than, i++.
...
So if you're writing i++ as a statement rather than as part of a larger
expression, why not just write ++i instead? You never lose anything, and
you sometimes gain something. Old line C programmers are used to writing
i++ instead of ++i. E.g., they'll say, for (i = 0; i < 10; i++) .... Since
this uses i++ as a statement, not as a part of a larger expression, then
you might want to use ++i instead.
</q>
Lots of people apparently imprinted on i++ because that's what K&R did,
but
there's no rational reason to cling to that preference in C++. I
programmed
in C extensively for about 9 years before moving to C++, and while I
always
wrote i++ per K&R, I instantly understood the C++ argument why ++i is
better when there's a choice, namely, "It never hurts, and it may help."
--
Doug Harrison
Visual C++ MVP