error: field has incomplete type

I have these three structures:

Code:

typedef uint32_t      LINX_SPID;


struct sockaddr_linx
{
        sa_family_t family;
        LINX_SPID   spid;
};

  typedef struct protocolstruct ProtocolStruct;
  struct protocolstruct
  {
      struct sockaddr_linx                     sin1,  
                                              sin2;   
      int                                   nodelay; 
      struct hostent                            *addr;  
      int                                    sndbufsz, 
                                              rcvbufsz; 
#if defined(INFINIBAND)
      IB_mtu_t                        ib_mtu;  
      int                                    commtype; 
      int                                    comptype; 
#endif
  };

typedef struct argstruct ArgStruct;
struct argstruct
{
   ...
   <lots of other irrelevant declarations>
   struct protocolstruct prot;
};

But, when I run the program, I get the error

Code:

 error: field 'prot' has incomplete type

and it is pointing to the line in blue.
The only thing that can cause problems in "prot" is
struct sockaddr_linx sin1, sin2;
But, the struct sockaddr_linx has been declared in the same file. Why am I getting this error?

I'm not sure about this, but what happens if you change this line:

struct protocolstruct prot;

to this:
protocolstruct prot;

Tried that , I get this message :

Code:

netpipe2.h:262: error: syntax error before 'ProtocolStruct'
netpipe2.h:262: warning: no semicolon at end of struct or union
netpipe2.h:264: warning: ISO C does not allow extra ';' outside of a function

Are they all in the same header file?
Are all the header file(s) included?
Are they included in the right order?

Surprisingly, I removed the first member in the structure "protocol struct", I am still getting the same error. This is absurd..

There was a
#ifdef(TCP) enclosing the whole protocol struct and I had to set the -DTCP flag when I tried to compile it
:|

Just out of curiosity,
>Are they included in the right order?
Does the order really matter. Is it compiler dependent? I have even noticed that I dont get any error/warning even if I include the same header file multiple times. Or is it got to do with the -Wall option?

That's because all standard header have "locks"

there like:

Code:

#ifndef __HEADER__
#define __HEADER__

code
code
code

#endif

Hmmm.. makes sense. What about re-declarations?

Originally Posted by kris.c

Hmmm.. makes sense. What about re-declarations?

What do you mean by "re-declarations"?

I get confused with declarations, definitions and etc :P

Sorry.. I should have typed , multiple inclusions instead..

do you mean multiple inclusions of header files?
they'll give you that "re-declarations" error that you mentioned.

To prevent a file from being included multiple no. of times, you can use the #pragma once directive or you can also use #include guard bands.
The #pragma directive is compilor specific (but I think #pragma once is supported by C99)
Google for more information.

regards,
koodoo