structs pointing to each other; compile problem

[Elise5]

Hei!

I have defined two structure types. Each has a parameter that is a pointer to the other structure, and, of course, it does not compile. How can I come over this problem? This structure definition will result in a very efficient coding, so I would like to keep it.
Example:

typedef struct Item_s{
int param1;
int param2;
std::list<EntryList_T::iterator> entryPtrList;
}Item_T;

typedef std::list<Item_T> ItemList_T;

typedef struct Entry_s{
uint id;
ItemList_T::iterator item_iter;
}Entry_T;

typedef std::list<Entry_T> EntryList_T;

[Skizmo]

Your answer is forward referencing.

// struct B is referenced

// this tells the compiler there is a struct B, but the compiler doesn't know
// what's in there. The compiler will resolve the content of struct B later.
typedef struct B; 


typedef struct _A
{
   B *ptrToStructB;
}A;

typedef struct _B
{
   A *ptrToStructA;
}B;

[Elise5]

Hi!

Thank you for your answer, but I cannot make it work. I get en error:

error: invalid redeclaration of type name "Entry_T" (declared at line 159)


Is this compiler dependent or ..?

[TSYS]

Skizmo made a typing error: the forward reference should be

struct B;

(without the "typedef").

[0xC0000005]

Forward referencing will not work unless you modify your code to use pointers as shown by Skizmo.

But even if you do use pointers I believe that it will still be impossible to use *EntryList_T::interator as a template argument. In order to know that EntryList_T has an iterator the class must be previously defined - the same problem you have now.

I would suggest re-thinking the problem to see if you can come up with a more elegant design for your application's data objects.

[Elise5]

Hello again and thank your for your help!

But, ... I cannot make forward reference work even if I make as simple as the example your had:

struct B;


typedef struct _A
{
B *ptrToStructB;
}A;

typedef struct _B
{
A *ptrToStructA;
}B;


I still get th error:

error: invalid redeclaration of type name "B" (declared at line 159)
}B;

So, is this something with the compiler (I use Intel 9.1) or a compiler option that I should change?

Regards,

Elise

[Ajay Vijay]

Try removing the 'typedef' altogether. You are 'forward' defining 'B' as plain struct (telling the compiler), and then you are using typedef keyword to define B (based on _B).

[Elise5]

Removing typedef helps.

It compiles now.

Thank you!

[Marc G]

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