Re: mutually referential (Pg 140 K&R2)

G Patel wrote: 
Pg. 140 of K&R2 shows an example of mutually referential structure
declarations...

struct t
{
    struct s *p;
};

struct s
{
    struct t *q;
};


I ran the following test program through my C compiler to see if it
would compile:

#include <stdlib.h>

struct t
{
    struct s *p;  /* type 'struct s' is not visible here */
};

struct s
{
    struct t *q;
};

int main()
{
    printf("Hello world\n");
    return 0;
}


It compiled and ran without any noticeable problems.  I expected it to
complain about the line I've commented above.

How is this valid when the type 'struct s' is not in scope when *p is
declared as a member of the type struct t?

If this is 'valid' please tell me why scopes don't apply here.  If this
is 'not  valid' please tell me how I can declare mutually referential
struct types.


struct s *p declares p using an incomplete struct s type, which is later completed
with struct s {...}. Incomplete types apply only to curly bracket things like
enums, unions, and structs iirc.
.

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