Re: basic question on c++ linking
On Jun 29, 2:03 pm, Erik Wikstr=F6m <Erik-wikst...@telia.com> wrote:
On 2008-06-29 13:10, Peskov Dmitry wrote:
Let me put my question differently ? which one below
a)
class new_class;
This is a declaration, it tells the compiler that there exists
a class called new_class, but nothing else. If all you need is
a pointer to the class a declaration is enough, for just about
anything else you need the definition too.
And references, of course.
Also, you can *declare* (but not define) objects of the type.
Thus, "extern new_class some_object ;" is legal with just a
class declaration. Or, within a class:
class Another
{
new_class illegal; // a non-static member is a definition
static new_class legal ;
// but a static member is just a
// declaration (which means that it
// must be defined elsewhere).
} ;
b)
class new_class
{
int a;
public:
new_class();
};
This is the definition, it tells the compiler what the
new_class is (how much memory an instance needs, what members
it has etc.). Notice that a definition is also a declaration,
you can declare a type as many times as you want but you can
only define it once.
In general. Classes (and templates and inline functions) are an
exception. You can only define them once in each translation
unit, but you can define them in as many translation units as
you want, as long as the definitions are identical.
[...]
I assume class definition includes the function that you are
defining something like
class new_class
{
int a;
public:
new_class();
};
new_class::new_class
{
a = 10;
}
No, that is the definition of the member function (the
constructor in this case),
I don't think so. To be the definition of the constructor, he'd
need to have parentheses after the second new_class.
--
James Kanze (GABI Software) email:james.kanze@gmail.com
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