How to allocate a static class attribute in c++?

[herman]

Hi,

I have a static class attribute in my class:

class A
{
public:
static B aB;
}

How can I allocate this static class attribute?

I think I need to do this

A::aB = ??? ;

If I do this:

A::aB = new B(); // where/when will aB be deleted if I allocate it on
the heap?

If I dont do anything, I have this linker error:

A.cpp:229: undefined reference to `A::aB'

 

[Victor Bazarov]

I have a static class attribute in my class:

class A
{
public:
static B aB;
}

;

And it's not really "an attribute", it's *a data member*.

How can I allocate this static class attribute?

I think I need to do this

A::aB = ??? ;

Close. You need to do

B A::aB;

if your 'B' class has a default constructor, or

B A::aB( ??? );

(replace ??? with proper constructor arguments) if your 'B' class
requires arguments for its construction.

If I do this:

A::aB = new B(); // where/when will aB be deleted if I allocate it on
the heap?

Don't. You need to un-learn your Java habits of using 'new' for
everything.

If I dont do anything, I have this linker error:

A.cpp:229: undefined reference to `A::aB'

Correct. You do need to define any static member (except if it has
a constant integral type and the address of it is never taken).

V

 

[Neelesh Bodas]

Hi,

I have a static class attribute in my class:

class A
{
public:
static B aB;

}

How can I allocate this static class attribute?

aB is a data member, not a pointer. You shouldnot call "new" for
allocating (as you did below)
Simply saying

B A::aB;

will work, provided the definition of B is in scope, and constructor
B::B() is callable.

I think I need to do this

A::aB = ??? ;

If I do this:

A::aB = new B(); // where/when will aB be deleted if I allocate it on
the heap?

you can't do this, since aB is not a pointer

If I dont do anything, I have this linker error:

A.cpp:229: undefined reference to `A::aB'

Finally, lookup "static initialization order fiesco" :
http://www.parashift.com/c++-faq-lite/ctors.html#faq-10.12

-N

 

[herman]

aB is a data member, not a pointer. You shouldnot call "new" for
allocating (as you did below)
Simply saying

B A::aB;

will work, provided the definition of B is in scope, and constructor
B::B() is callable.







you can't do this, since aB is not a pointer



Finally, lookup "static initialization order fiesco" :http://www.parashift.com/c++-faq-lite/ctors.html#faq-10.12

-N

Thanks a lot for both answers!