Silly Q about circular references

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10-04-2006
ppmoore

Silly Q about circular references

Hello,

I have a silly question about circular references in C (note: not C++):

typedef void ( *FSM ) ( CALL_CB* );

typedef struct _fsm_cb
{

FSM fsm_entry;
} FSM_CB;

typedef struct _call_cb
{

FSM_CB *fsm;
} CALL_CB;

int main()
{

CALL_CB* call_cb;

return 1;
}
This can't compile because FSM_CB is referencing CALL_CB and vice versa:

test.c:4: syntax error before '*' token

I know that C++ has a solution to this, by simply declaring the second class before the first:

class Second;
class First
{

Second* m_second;
};
class Second
{

First* m_first;
};

main ()
{

First* aFirst;
Second* aSecond;
}

Can anyone help?

Thanks,
Paul
10-04-2006
Prelude

>I know that C++ has a solution to this, by simply declaring the second class before the first
C has the same solution. :)
10-04-2006
SKeane

Code:

struct _call_cb; typedef void ( *FSM ) ( struct _call_cb* ); typedef struct _fsm_cb { FSM fsm_entry; } FSM_CB; typedef struct _call_cb { FSM_CB *fsm; } CALL_CB; int main() { CALL_CB* call_cb; return 1; }

Possibly
10-04-2006
ppmoore

I had tried that, still doesn't work:

struct _call_cb;

typedef void ( *FSM ) ( CALL_CB* );

...

test.c:3: syntax error before '*' token

Any other ideas?
Paul
10-04-2006
SKeane

Try reading what I actually posted?

I've highlighted the bit you missed.
10-04-2006
ppmoore

Oops, thanks SKeane.

That worked! Great!
Paul
10-04-2006
SKeane

Not saying it'll work mind!
10-04-2006
dwks

You could also put the typedef beforehand (at least I think so, and Dinkumware does too):

Code:

typedef struct _call_cb CALL_CB; typedef void ( *FSM ) ( CALL_CB* ); typedef struct _fsm_cb { FSM fsm_entry; } FSM_CB; struct _call_cb { FSM_CB *fsm; }; int main() { CALL_CB* call_cb; return 1; }
10-04-2006
CornedBee

Yes, that's valid. I would have posted it, but I was too lazy.