Re: Leak or Crash. Don't understand why

From:

Luk Jack <jlluckie7156468@gmail.com>

Newsgroups:

microsoft.public.vc.language

Date:

Thu, 10 Jun 2010 04:38:26 -0700 (PDT)

Message-ID:

<c09f3463-78c7-4aaa-b548-b1eebb24116f@z13g2000prh.googlegroups.com>

On 6=E6=9C=8810=E6=97=A5, =E4=B8=8B=E5=8D=887=E6=99=8209=E5=88=86, Ulrich E=
ckhardt <eckha...@satorlaser.com> wrote:

Luk Jack wrote:

/// Test cMath
double ans = 1.0f;
cMath *m = new cMath();

ans = m->Power(3,2);
Formula fTest;
fTest.resize(2);
fTest[0].coefficient = 2;
fTest[0].degree = 3;

fTest[1].coefficient = 2;
fTest[1].degree = 1;

m->Derive(fTest);

fTest = m->getFormula();

if (m) {
delete m; // Leak (if absent) or Crash (if present)
m = NULL;
}

Several points here:
1. Wrapping something into a class that only contains functions and no
actual state (which is what your cMath class looks like, though I'm not
sure) is wrong. If you need, use a namespace instead. I guess you have th=

habit and probably a few others from Java or similar languages that force
you to use classes for everything.
2. Don't dynamically allocate things unless you have a good reason to. Ju=

create a local instance of class cMath if you need.
3. If you really need dynamically allocated objects, use a "smart pointer=

to automatically delete them - C++ doesn't have a garbage collector.
std::auto_ptr would be one, the other would be std::tr1::shared_ptr or
boost::shared_ptr. Note that the former guarantees exclusive ownership
while the other models shared ownership.
4. You don't have to check a pointer before invoking delete on it.

Summary: The problem is in the code you don't show.

Uli

--
C++ FAQ:http://parashift.com/c++-faq-lite

Sator Laser GmbH
Gesch=C3=A4ftsf=C3=BChrer: Thorsten F=C3=B6cking, Amtsgericht Hamburg HR =

B62 932

Actually, I've got an attribute in my cMath class, so isn't it
stateless, is it? not too sure :)
Thanks
Jack