Обсуждение: forward declaration in c

Hello

I can't to find fine syntax for cyclic declaration:

.
typedef Node *(*TransformColumnRef_hook_type) (ParseState *pstate,
ColumnRef *cref);

typedef struct ParseState
{       struct ParseState *parentParseState;            /* stack link */       const char *p_sourcetext;       /*
sourcetext, or NULL if not 
available */       List       *p_rtable;           /* range table so far */       List       *p_joinexprs;        /*
JoinExprsfor RTE_JOIN 
p_rtable entries */       List       *p_joinlist;         /* join items so far (will
become FromExpr                                                                *
node's fromlist) */       List       *p_relnamespace; /* current namespace for relations */       List
*p_varnamespace;/* current namespace for columns */       List       *p_ctenamespace; /* current namespace for common 
table exprs */       List       *p_future_ctes;      /* common table exprs not yet
in namespace */       List       *p_windowdefs;       /* raw representations of
window clauses */       Oid                *p_paramtypes;       /* OIDs of types for
$n parameter symbols */       int                     p_numparams;    /* allocated size of
p_paramtypes[] */       int                     p_next_resno;   /* next targetlist
resno to assign */       List       *p_locking_clause;           /* raw FOR UPDATE/FOR
SHARE info */       Node       *p_value_substitute;         /* what to replace
VALUE with, if any */       bool            p_variableparams;       bool            p_hasAggs;       bool
p_hasWindowFuncs;      bool            p_hasSubLinks;       bool            p_is_insert;       bool
p_is_update;      Relation        p_target_relation;       RangeTblEntry *p_target_rangetblentry;
TransformColumnRef_hook_type   transformColumnRef_hook; 
} ParseState;

with empty declaration typedef struct ParseState;

I got errors:
In file included from ../../../src/include/catalog/heap.h:18,                from parse_clause.c:20:
../../../src/include/parser/parse_node.h:79: warning: useless storage
class specifier in empty declaration
../../../src/include/parser/parse_node.h:81: error: expected ‘)’
before ‘*’ token
../../../src/include/parser/parse_node.h:109: error: expected
specifier-qualifier-list before ‘TransformColumnRef_hook_type’

thank you
Pavel

On Mon, May 25, 2009 at 01:20:05PM +0200, Pavel Stehule wrote:
> Hello
>
> I can't to find fine syntax for cyclic declaration:

If you mean forward declaraions of a type, just:

struct ParseState

will do, then:

> typedef Node *(*TransformColumnRef_hook_type) (struct ParseState *pstate,
> ColumnRef *cref);

With the "struct" keyword added.

> with empty declaration typedef struct ParseState;

It might work with:

typedef struct ParseState ParseState;

But then you can't use typedef in the actual declaraion (AFAIK you can
only forward declare structs, enums and such, but not typedefs).

Have a nice day,
--
Martijn van Oosterhout   <kleptog@svana.org>   http://svana.org/kleptog/
> Please line up in a tree and maintain the heap invariant while
> boarding. Thank you for flying nlogn airlines.

2009/5/25 Martijn van Oosterhout <kleptog@svana.org>:
> On Mon, May 25, 2009 at 01:20:05PM +0200, Pavel Stehule wrote:
>> Hello
>>
>> I can't to find fine syntax for cyclic declaration:
>
> If you mean forward declaraions of a type, just:
>
> struct ParseState
>
> will do, then:
>
>> typedef Node *(*TransformColumnRef_hook_type) (struct ParseState *pstate,
>> ColumnRef *cref);
>
> With the "struct" keyword added.
>
>> with empty declaration typedef struct ParseState;
>

yes, good advice

thank you
Pavel

> It might work with:
>
> typedef struct ParseState ParseState;
>
> But then you can't use typedef in the actual declaraion (AFAIK you can
> only forward declare structs, enums and such, but not typedefs).
>
> Have a nice day,
> --
> Martijn van Oosterhout   <kleptog@svana.org>   http://svana.org/kleptog/
>> Please line up in a tree and maintain the heap invariant while
>> boarding. Thank you for flying nlogn airlines.
>
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