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From: MC on 3 Mar 2010 03:40
Say I have the following classes

class A{};
class B{};
class C{};

class X{
A* a;
B* b;
C* c;
public:
X() : a(new A), b(new B), c(new C) {}
};

Say now new fails while initializing C. Since X is not constructed
completely it will not call its destructor and we will have a and b
never destructed and hence a memory leak.
What is the best way to avoid this problem.

Should I never use new in the constructor?

Thanks


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From: Francis Glassborow on 3 Mar 2010 08:55
MC wrote:
> Say I have the following classes
>
> class A{};
> class B{};
> class C{};
>
> class X{
> A* a;
> B* b;
> C* c;
> public:
> X() : a(new A), b(new B), c(new C) {}
> };
>
> Say now new fails while initializing C. Since X is not constructed
> completely it will not call its destructor and we will have a and b
> never destructed and hence a memory leak.
> What is the best way to avoid this problem.

By not using raw pointers to hold onto dynamic resources (use a suitable
smart pointer)

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From: peter koch larsen on 3 Mar 2010 09:07
On 3 Mar., 21:40, MC <manan.cho...(a)gmail.com> wrote:
> Say I have the following classes
>
> class A{};
> class B{};
> class C{};
>
> class X{
> A* a;
> B* b;
> C* c;
> public:
> X() : a(new A), b(new B), c(new C) {}
>
> };
>
> Say now new fails while initializing C. Since X is not constructed
> completely it will not call its destructor and we will have a and b
> never destructed and hence a memory leak.
> What is the best way to avoid this problem.
>
> Should I never use new in the constructor?

Not if you have more than one. You get around this problem by using
auto_ptr:
X()
{
auto_ptr<A> aa(new A);
auto_ptr<B> ab(new B);
a = aa.release();
b = ab.release();
}

You will have to expand the example to three parameters. ;-)

/Peter


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From: Stuart Golodetz on 3 Mar 2010 17:20
MC wrote:
> Say I have the following classes
>
> class A{};
> class B{};
> class C{};
>
> class X{
> A* a;
> B* b;
> C* c;
> public:
> X() : a(new A), b(new B), c(new C) {}
> };
>
> Say now new fails while initializing C. Since X is not constructed
> completely it will not call its destructor and we will have a and b
> never destructed and hence a memory leak.
> What is the best way to avoid this problem.
>
> Should I never use new in the constructor?
>
> Thanks

See FAQ 17.4:

http://www.parashift.com/c++-faq-lite/exceptions.html#faq-17.4

The executive summary is that you should replace those raw pointers with
smart pointers and your problem will go away.

Regards,
Stu

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From: Johannes Schaub (litb) on 3 Mar 2010 17:19
MC wrote:

> Say I have the following classes
>
> class A{};
> class B{};
> class C{};
>
> class X{
> A* a;
> B* b;
> C* c;
> public:
> X() : a(new A), b(new B), c(new C) {}
> };
>
> Say now new fails while initializing C. Since X is not constructed
> completely it will not call its destructor and we will have a and b
> never destructed and hence a memory leak.
> What is the best way to avoid this problem.
>
> Should I never use new in the constructor?
>

Use smart pointers:

class X{
shared_ptr<A> a;
shared_ptr<B> b;
shared_ptr<C> c;
public:
X() : a(new A), b(new B), c(new C) {}
};

The initialization of each member is separately from each other member, so
you are guaranteed that as long as "a" is not yet completely initialized,
the "new B" has not yet been done. On the other side, if something here
throws, any completely constructed member is destructed again. So you no
longer leak memory.

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