FIL

The FIL structure (file object) holds the state of an open file. It is created by f_open function and discarded by f_close function. Application program must not modify any member in this structure except for cltbl, or any data on the FAT volume can be collapsed. Note that a sector buffer is defined in this structure at non-tiny configuration (_FS_TINY == 0), so that the FIL structures at that configuration should not be defined as auto variable.

typedef struct {
    FATFS*  fs;           /* Pointer to the owner file system object */
    WORD    id;           /* Owner file system mount ID */
    BYTE    flag;         /* File object status flags */
    BYTE    err;          /* Abort flag (error code) */
    DWORD   fptr;         /* File read/write pointer (Byte offset origin from top of the file) */
    DWORD   fsize;        /* File size in unit of byte */
    DWORD   sclust;       /* File start cluster */
    DWORD   clust;        /* Current cluster of fptr (One cluster behind if fptr is on the cluster boundary. Invalid if fptr == 0.) */
    DWORD   dsect;        /* Current data sector (Can be invalid if fptr is on the cluster boundary.)*/
#if !_FS_READONLY
    DWORD   dir_sect;     /* Sector number containing the directory entry */
    BYTE*   dir_ptr;      /* Ponter to the directory entry in the window */
#endif
#if _USE_FASTSEEK
    DWORD*  cltbl;        /* Pointer to the cluster link map table (Nulled on file open. Set by application.) */
#endif
#if _FS_LOCK
    UINT    lockid;       /* Fle lock ID */
#endif
#if !_FS_TINY
    BYTE    buf[_MAX_SS]; /* File private data transfer buffer (Always valid if fptr is not on the sector boundary but can be invalid if fptr is on the sector boundary.) */
#endif
} FIL;