Thread: Forward declaration of structs?

Code:

struct Request;

struct Requester
{
	bool beingServiced;
	list<Request> requests;
};

struct Request
{
	Requester r;
	int track;
};

you mean like that?
I'm not sure that will work for whole objects and not pointers or referencies...

It seems that incomplete types are not allowed to be used as list template argument.

You may need to put Request before Requester, forward declare Requester and replace the r member with Requester* (why does request hold a requester by value?)

Is the first even legal? Unless, of course, list only references the struct via pointers or references, of course, and seeing as it is a std::list, that makes sense...

List holds copies of the instances if I'm not mistaken

In any case, Comeau online says this:

Code:

"concept_checks.h", line 555: error: incomplete type is not allowed
    static void _Assignable_requirement_violation(_Type __a) {
                                                  ^
          detected during instantiation of "void
                    _Assignable_concept_specification<_Type>::_Assignable_requi
                    rement_violation(_Type) [with _Type=Request]" at line 8 of
                    "ComeauTest.c"

Code:

#include <list>
struct Request;

struct Requester
{
	bool beingServiced;
	std::list<Request> requests;
};

struct Request
{
	Requester r;
	int track;
};

MinGW and VC++ appear to compile it without errors, though.

The standard also says that using an incomplete type as the type of a container is undefined behavior. (17.4.3.6p2)

Originally Posted by jcafaro10

It probably isn't. I'm new to C++ and for a project I'm doing I have a list of Requestors each having their own Requests. The Requests have to know where they came from. This seemed the easiest way to do it.

Then clearly, you need a pointer to the requestor that it came from, not a copy of the requestor.

--
Mats

But the requests don't know where they are coming from, do they? Instead they create a totally new and unrelated Requester instance...

If the contained object need to know about its owner, you do need a pointer (or reference) to it. And then you should be able to forward declare it the other way round...