C++ is slow

[Charles Herman]

I have the following two programs:

PROG I
void main()
{
int *v = new int[NUM];
for (int i = 0; i < NUM; ++i)
v[i] = i;
}

PROG II
class rvector
{
private:
int* vals;
size_t vsize;

public:
explicit rvector( size_t vSize ) { vals = new int[vsize]; }
~rvector() { delete [] vals; }

int& operator[] (size_t idx ) { return vals[idx]; }
};

void main()
{
rvector v(NUM);
for (i = 0; i < NUM; ++i)
v[i] = i;
}

I left out some non-germane lines, eg, defining NUM and including header
files.

I compiled and ran these programs using VC++ 6.0. The second program
required approx 6 times as much time to run as the first. What is happening
in program II that takes so much time?

-charles

[Mike Wahler]

"Charles Herman" <ch*****@no.spa m> wrote in message
news:PO62c.1206 45$Xp.533671@at tbi_s54...

I have the following two programs:

PROG I
void main()
int main()

If you use anything else besides 'int' return type
for main, you have *no* guarantees about the behavior of
your program.
{
int *v = new int[NUM];
for (int i = 0; i < NUM; ++i)
v[i] = i;
You have a memory leak. You need to free the memory
you allocate.
}

PROG II
class rvector
{
private:
int* vals;
size_t vsize;

public:
explicit rvector( size_t vSize ) { vals = new int[vsize]; }
~rvector() { delete [] vals; }

int& operator[] (size_t idx ) { return vals[idx]; }
};

void main()
And again.
{
rvector v(NUM);
for (i = 0; i < NUM; ++i)
v[i] = i;
}

I left out some non-germane lines, eg, defining NUM and including header
files.
You should always strive to post *compilable* code if at all
possible. Then we needn't guess at the rest, which is often
the cause of a stated problem.

I compiled and ran these programs using VC++ 6.0. The second program
required approx 6 times as much time to run as the first. What is happening in program II that takes so much time?

The C++ language is a set of specifications, an abstraction.
I has no 'speed', slow or fast. Apparently you find a particular
*implementation * of C++, (VC++6.0) "too slow".

Recommended actions:

Read your documentation to ensure you're using the product correctly,
and find it's various 'modes' of operation.

If VC++ is deemed unacceptable, use something else.

-Mike

[Mike Wahler]

"Mike Wahler" <mk******@mkwah ler.net> wrote in message
news:OT******** **********@news read2.news.pas. earthlink.net.. .

"Charles Herman" <ch*****@no.spa m> wrote in message
news:PO62c.1206 45$Xp.533671@at tbi_s54...

I have the following two programs: [snip]
{
int *v = new int[NUM];
for (int i = 0; i < NUM; ++i)
v[i] = i;
[snip]
PROG II
class rvector
{
private:
int* vals;
size_t vsize;

public:
explicit rvector( size_t vSize ) { vals = new int[vsize]; }
~rvector() { delete [] vals; }

int& operator[] (size_t idx ) { return vals[idx]; }
};

[snip]
{
rvector v(NUM);
for (i = 0; i < NUM; ++i)
v[i] = i;
}

You're comparing two different things, naturally their
behavior will often be different. Your 'rvector' class
does more work than your first example.

You're comparing "apples vs oranges".

-Mike

[Leor Zolman]

On Fri, 05 Mar 2004 22:03:27 GMT, "Charles Herman" <ch*****@no.spa m> wrote:

I have the following two programs:

PROG I
void main()
{
int *v = new int[NUM];
for (int i = 0; i < NUM; ++i)
v[i] = i;
}

PROG II
class rvector
{
private:
int* vals;
size_t vsize;

public:
explicit rvector( size_t vSize ) { vals = new int[vsize]; }
I'd look real hard at the spelling of those various version of vsize you
have there. What do you think the value of 'vsize' above really is? ;-)

[plus all of Mike's remarks]
-leor
~rvector() { delete [] vals; }

int& operator[] (size_t idx ) { return vals[idx]; }
};

void main()
{
rvector v(NUM);
for (i = 0; i < NUM; ++i)
v[i] = i;
}

I left out some non-germane lines, eg, defining NUM and including header
files.

I compiled and ran these programs using VC++ 6.0. The second program
required approx 6 times as much time to run as the first. What is happening
in program II that takes so much time?

-charles

Leor Zolman
BD Software
le**@bdsoft.com
www.bdsoft.com -- On-Site Training in C/C++, Java, Perl & Unix
C++ users: Download BD Software's free STL Error Message
Decryptor at www.bdsoft.com/tools/stlfilt.html

[Aggro]

Charles Herman wrote:

I have the following two programs:

PROG I
void main()
int main()
{
int *v = new int[NUM];
for (int i = 0; i < NUM; ++i)
v[i] = i;

Did you forget something? delete [] v; perhaps? We don't want to cause
memory leaks, do we?

You will also want to put return 0; at the end of main, because VC 6.0
has a bug and it will complain about int main() if you don't use that. (
It is not required by the standard, but it doesn't matter if you use it.
I personally think that it is even better to use it. )

return 0;
}

PROG II ~rvector() { delete [] vals; }
Note that here you are using delete, unlike you did with the first
program. This might be causing some of the time difference.
int& operator[] (size_t idx ) { return vals[idx]; }
};

void main()
int main()
{
rvector v(NUM);
for (i = 0; i < NUM; ++i)
v[i] = i;
return 0;
}

I left out some non-germane lines, eg, defining NUM and including header
files.

Don't do that they might contain some valuable information.

[Andrey Tarasevich]

Charles Herman wrote:

...
I compiled and ran these programs using VC++ 6.0. The second program
required approx 6 times as much time to run as the first. What is happening
in program II that takes so much time?
...

Firstly, I compiled your program with VC6 and run it. Both cycles take
the same time to run, which is not surprising since both cycles are
compiled into identical code. You must be doing something incorrectly,
like testing debugging configuration of the code, which is meaningless.

Secondly, aside from some minor errors (like 'void main'), both programs
are valid C++ programs. Whatever the results are, this test cannot be
used to show that "C++ is slow".

--
Best regards,
Andrey Tarasevich

[Leor Zolman]

On Fri, 05 Mar 2004 22:12:09 GMT, "Mike Wahler" <mk******@mkwah ler.net>
wrote:

You're comparing two different things, naturally their
behavior will often be different. Your 'rvector' class
does more work than your first example.
You have no idea now /much/ more work... (sorry, Mike, couldn't resist)
-leor

You're comparing "apples vs oranges".

-Mike

Leor Zolman
BD Software
le**@bdsoft.com
www.bdsoft.com -- On-Site Training in C/C++, Java, Perl & Unix
C++ users: Download BD Software's free STL Error Message
Decryptor at www.bdsoft.com/tools/stlfilt.html

[Mike Wahler]

"Leor Zolman" <le**@bdsoft.co m> wrote in message
news:t4******** *************** *********@4ax.c om...

On Fri, 05 Mar 2004 22:12:09 GMT, "Mike Wahler" <mk******@mkwah ler.net>
wrote:

You're comparing two different things, naturally their
behavior will often be different. Your 'rvector' class
does more work than your first example.

You have no idea now /much/ more work...

Um yes, I do. (or was that directed at OP?)

-Mike

[Rolf Magnus]

Mike Wahler wrote:

You're comparing "apples vs oranges".

http://www.inno-vet.com/articles/1999/0599/52.htm

[Mike Wahler]

"Rolf Magnus" <ra******@t-online.de> wrote in message
news:c2******** *****@news.t-online.com...

Mike Wahler wrote:

You're comparing "apples vs oranges".

http://www.inno-vet.com/articles/1999/0599/52.htm

In his experiment, he chemically and physically changes both
the apple and the orange. So he no longer has an apple or
an orange for comparison.

Also he's protesting that folks are using "apples vs organges"
to denigrate[sic] someone else's analogy. OP did not make an
analogy, I only used one to refute his complaint about
two *different* code examples.
-Mike