| re: "syntax error: identifier" instantiating another class within samenamespace?
Stephen Corey wrote:[color=blue]
> Carl Daniel [VC++ MVP] wrote:[color=green]
>> Stephen Corey wrote:
>>[color=darkred]
>>> I've got 2 classes in 2 seperate header files, but within the same
>>> namespace. If I use a line like:
>>>
>>>
>>> // This code is inside Class2's header file
>>> Class1 *newitem = new Class1(param1, param2);
>>>
>>>
>>> I get "syntax error: identifier" and "undeclared identifier". Since
>>> they're in the same namespace, and even in the same project, do I
>>> need to do anything special, like put an "#include <theotherfile.h>" in
>>> each header or anything???[/color]
>>
>>
>> Yes.
>>
>> The compiler only every looks at one file at a time. If you're
>> compiling x.cpp, the compiler sees x.cpp and everything that it
>> includes (directly or indirectly) in the order that it's included.
>> Anything that you reference must have been declared (and possibly
>> defined) before the point of reference.
>>
>> Generally speaking, if you have mutually dependent classes, you'll
>> have to "forward declare" one of the classes. Any decent C++ book
>> will cover the necessities.
>>
>> -cd
>>
>>[/color]
>
> Thanks for the response!
>
> What if each class references the other one (circular references). How
> would you handle that?[/color]
class X;
class Y
{
X* m_X;
};
class X
{
Y* m_y;
};
If you need member functions of the classes to access members of the "other
type", you'll need to define your class implementation outside the class
definition:
struct X
{
int m_i;
void useY();
};
struct Y
{
int m_j;
void useX();
};
void X::useY()
{
Y y;
y.m_j;
}
void Y::useX()
{
X x;
x.m_i;
}
A "forward declaration" (or "incomplete class declaration" in standardese)
allows you to refer to a class in contexts that don't require knowing the
size or interface of a class (such as declaring a pointer or reference
variable or parameter). In order to declare a variable of the class type,
or access any members of the class, a complete class is required.
Between forward declarations and out of line member definitions, you should
be able to handle any sensible mutual dependency.
-cd
| 
