Need help understanding info in a header file

i am trying to figure out what is the IFilePtr? (int, pointer, char?)

Code:

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/* filesys - header information file system interface */
/*  $Id: filesys.h,v 1.97.4.4.2.3 2003/02/04 16:51:47 mark Exp $  */

#ifndef        ACU_FSI_FILESYS_H
#define        ACU_FSI_FILESYS_H

/*
** LargeFileOff_t should be "long" or "off64_t" for UNIX systems, and
** "__int64" for Windows.
*/
#ifndef LargeFileOff_t
#ifdef  WIN32
/* Win32 API */
#define LargeFileOff_t  __int64
#else  /* WIN32 */
/* UNIX API */
#ifdef        HAVE_LARGE_FILE_API
#define LargeFileOff_t  off64_t
#else        /* HAVE_LARGE_FILE_API */
#define LargeFileOff_t  long
#endif        /* HAVE_LARGE_FILE_API */
#endif  /* WIN32 */
#endif  /* LargeFileOff_t */

/* Define PROTOTYPE if your compiler understands ANSI-style prototypes */
#ifndef        P_
#ifdef  PROTOTYPE
#define P_(x)  x
#else  /* PROTOTYPE */
#define P_(x)  ()
#endif  /* PROTOTYPE */
#endif        /* P_ */

/* Allow "region locks" (ie, record locks that are applied to the        */
/* entire record) by setting WANT_REGION_LOCKS to "1".  Region locks        */
/* improve performance in cases where very many locks are applied in a        */
/* file at once (because adjacent record locks will collapse into a        */
/* single lock region in the Unix lock manager).  */

#define        WANT_REGION_LOCKS        0

#if        WANT_REGION_LOCKS
#ifdef        O_UNIX
#ifndef        ENFORCED_LOCKS
#define        REGION_LOCKS_OK
#endif        /* ENFORCED_LOCKS */
#endif        /* O_UNIX */
#endif        /* WANT_REGION_LOCKS */

typedef        struct _i_abilities {
        unsigned        has_previous : 1;
        unsigned        alternate_collate : 1;
} I_ABILITIES;

#ifdef        __cplusplus
extern "C" {
#endif        /* __cplusplus */

#ifdef        INTERNAL_USE

typedef        struct _i_file                *IFilePtr;
typedef        struct _r_file                *RFilePtr;
typedef        struct _s_file                *SFilePtr;

#ifndef        ACU_GENERIC_PROC_DEFINED
/* generic proc for registering functions */
typedef int            (*GenericProc)();
#define        ACU_GENERIC_PROC_DEFINED
#endif        /* ACU_GENERIC_PROC_DEFINED */

typedef        int                (*FSIInitProc) P_((int, int *));
typedef        void                (*FSIExitProc) P_((void));
typedef        int                (*FSIMakeProc) P_((char *, char *, char *, char *, char *, char *));
typedef        IFilePtr        (*FSIOpenProc) P_((char *, int, char *));
typedef        int                (*FSICloseProc) P_((IFilePtr));
typedef        unsigned        (*FSIReadProc) P_((IFilePtr, char *, int));
typedef        unsigned        (*FSINextProc) P_((IFilePtr, char *));
typedef        unsigned        (*FSIPreviousProc) P_((IFilePtr, char *));
typedef        int                (*FSIStartProc) P_((IFilePtr, char *, int, int, int));
typedef        int                (*FSIWriteProc) P_((IFilePtr, char *, unsigned));
typedef        int                (*FSIRewriteProc) P_((IFilePtr, char *, unsigned));
typedef        int                (*FSIDeleteProc) P_((IFilePtr, char *));
typedef        int                (*FSIUnlockProc) P_((IFilePtr));
typedef        int                (*FSIInfoProc) P_((IFilePtr, int, char *));
typedef        void                (*FSISyncProc) P_((int));
typedef        int                (*FSIRemoveProc) P_((char *));
typedef        int                (*FSIRenameProc) P_((char *, char *));
typedef        int                (*FSIVersionProc) P_((char *, char *, char *, int, long *));
typedef        void                (*FSIAbilitiesProc) P_((I_ABILITIES *));
typedef        int                (*FSIExecuteProc) P_((char *, char *));
typedef        int                (*FSICopyProc) P_((char *, char *));
typedef        int                (*FSIBeginProc) P_((void));
typedef        int                (*FSICommitProc) P_((int));
typedef        int                (*FSIRollbackProc) P_((int));
typedef        int                (*FSIRecoverProc) P_((void));
typedef        GenericProc        (*FSIRegisterProc) P_((char *, GenericProc));
typedef        void                (*FSIInitConfigProc) P_((void));

typedef        int                (*FSI_RInitProc) P_((void));
typedef        void                (*FSI_RExitProc) P_((void));
typedef        int                (*FSI_RMakeProc) P_((char *, char *, long));
typedef        RFilePtr        (*FSI_ROpenProc) P_((char *, int, unsigned,
                                            unsigned, long));
typedef        int                (*FSI_RUnlockProc) P_((RFilePtr));
typedef        int                (*FSI_RCloseProc) P_((RFilePtr));
typedef        unsigned        (*FSI_RReadProc) P_((RFilePtr, char *, long));
typedef        unsigned        (*FSI_RNextProc) P_((RFilePtr, char *));
typedef        unsigned        (*FSI_RPreviousProc) P_((RFilePtr, char *));
typedef        int                (*FSI_RStartProc) P_((RFilePtr, long, int));
typedef        int                (*FSI_RWriteProc) P_((RFilePtr, char *, unsigned,
                                              long));
typedef        int                (*FSI_RDeleteProc) P_((RFilePtr, long));
typedef        int                (*FSI_RRewriteProc) P_((RFilePtr, char *, unsigned,
                                                long));
typedef        int                (*FSI_RRemoveProc) P_((char *));
typedef        int                (*FSI_RRenameProc) P_((char *, char *));
typedef        int                (*FSI_RCopyProc) P_((char *, char *));
typedef        int                (*FSI_RInfoProc) P_((RFilePtr, int, char *));

typedef        int                (*FSI_SMakeProc) P_((char *, char *));
typedef        SFilePtr        (*FSI_SOpenProc) P_((char *, int, unsigned, int,
                                            unsigned, int, char *, int));
typedef        int                (*FSI_SCloseProc) P_((SFilePtr, int));
typedef        int                (*FSI_SReadProc) P_((SFilePtr, char *));
typedef        int                (*FSI_SWriteProc) P_((SFilePtr, char *, unsigned, int));
typedef        int                (*FSI_SRewriteProc) P_((SFilePtr, char *, unsigned));
typedef        int                (*FSI_SRemoveProc) P_((char *));
typedef        int                (*FSI_SRenameProc) P_((char *, char *));
typedef        int                (*FSI_SCopyProc) P_((char *, char *));
typedef        LargeFileOff_t        (*FSI_SSeekProc) P_((SFilePtr, LargeFileOff_t, int));
typedef        int                (*FSI_SInfoProc) P_((SFilePtr, int, char *));

typedef        struct _i_dispatch {
        /*  Indexed file functions  */
        FSIInitProc                p_init;
        FSIExitProc                p_exit;
        FSIMakeProc                p_make;
        FSIOpenProc                p_open;
        FSICloseProc                p_close;
        FSIReadProc                p_read;
        FSINextProc                p_next;
        FSIPreviousProc                p_previous;
        FSIStartProc                p_start;
        FSIWriteProc                p_write;
        FSIRewriteProc                p_rewrite;
        FSIDeleteProc                p_delete;
        FSIUnlockProc                p_unlock;
        FSIInfoProc                p_info;
        FSISyncProc                p_sync;
        FSIRemoveProc                p_remove;
        FSIRenameProc                p_rename;
        FSIVersionProc                p_version;
        FSIAbilitiesProc        p_abilities;
        FSIExecuteProc                p_execute;
        FSICopyProc                p_copy;
        FSIBeginProc                p_begin;
        FSICommitProc                p_commit;
        FSIRollbackProc                p_rollback;
        FSIRecoverProc                p_recover;

        /*  Setup functions  */
        FSIRegisterProc                p_register;
        FSIInitConfigProc        p_init_cfg;

        /*  Relative file functions  */
        FSI_RInitProc                pr_init;
        FSI_RExitProc                pr_exit;
        FSI_RMakeProc                pr_make;
        FSI_ROpenProc                pr_open;
        FSI_RUnlockProc                pr_unlock;
        FSI_RCloseProc                pr_close;
        FSI_RReadProc                pr_read;
        FSI_RNextProc                pr_next;
        FSI_RPreviousProc        pr_previous;
        FSI_RStartProc                pr_start;
        FSI_RWriteProc                pr_write;
        FSI_RDeleteProc                pr_delete;
        FSI_RRewriteProc        pr_rewrite;
        FSI_RRemoveProc                pr_remove;
        FSI_RRenameProc                pr_rename;
        FSI_RCopyProc                pr_copy;
        FSI_RInfoProc                pr_info;

        /*  Sequential file functions  */
        FSI_SMakeProc                ps_make;
        FSI_SOpenProc                ps_open;
        FSI_SCloseProc                ps_close;
        FSI_SReadProc                ps_read;
        FSI_SWriteProc                ps_write;
        FSI_SRewriteProc        ps_rewrite;
        FSI_SRemoveProc                ps_remove;
        FSI_SRenameProc                ps_rename;
        FSI_SCopyProc                ps_copy;
        FSI_SSeekProc                ps_seek;
        FSI_SInfoProc                ps_info;
} I_DISPATCH;

typedef        int                (*FSI_IGetDispatchTableProc) P_((I_DISPATCH **));


#else        /* INTERNAL_USE */

struct _AcuFile_ {
        long        notused;
};

typedef        struct _AcuFile_        *IFilePtr;
typedef        struct _AcuFile_        *RFilePtr;
typedef        struct _AcuFile_        *SFilePtr;

#endif        /* INTERNAL_USE */

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Trimming some of the middle,

Code:

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#ifdef        INTERNAL_USE
typedef        struct _i_file                *IFilePtr;
#else
typedef        struct _AcuFile_        *IFilePtr;
#endif

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So it's a pointer to a structure of one type or another.

what are those? struct of what?

Why are you trying to look up the skirt of your implementation?

but i havent been able to determine what it is that i am trying to retreive from the actuall DLL involved.

a function v5_open() returns an IFilePtr but i cant get it to work.

Looks like some sort of COM-like wrapper on top of file IO to me.

They may never define that structure (though you can try recursively greping for '_i_file' in the include tree). It's defined in this header as an anonymous structure.

Part of the joy of making complicated DLL or SO files like this is that you can hide the details of whatever an '_i_file' is from the end user, so the DLL or SO file can be replaced without breaking the things that attempt to use it. Its contents probably aren't in your debug symbols, either.

As long as only 'I_DISPATCH' struct, and 'FSI_IGetDispatchTableProc' remain the same, the library can be upgraded without breaking your application. If you start using hidden members from that data, your own app is almost guaranteed to stop working as soon as somebody upgrades that library.

Quote:

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a function v5_open() returns an IFilePtr but i cant get it to work.

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Can you show us exactly how you're trying to use it? How are you declaring your IFilePtr variable? And what's your statement look like where you make the call to v5_open()? And how exactly can't you get it to work? Is it giving a compile error or run-time error? What's the error say?

within a delphi program. with the help of the vendor. they sent me the .h, .lib, & .dll files as well as the .c sample file. after we talked for a little while they decided that v5_open returns a pointer IFilePtr. so supposedly i can assign v5_open to a IFilePtr.

delphi implementation:
function v5_open(pChar, int, pChar): IFilePtr; cdecl, external 'adll.dll';

the problem is that it is always nil(null) when i try to load an IFilePtr.

I don't know the context of what you're doing, however if the call to v5_open() is returning nil (or NULL), there's probably something wrong with your call to v5_open() (the open is failing for some reason). You might want to try perror(), or at least looking at errno, since I'm guessing that v5_open() will set this on failure to indicate why it failed.

You should not have to know anything about IFilePtr other than it's what's returned by v5_open() and expected by various other library functions (v5_write(), v5_read(), v5_close()?)