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 the FAT volume will be collapsed. Note that a sector buffer is defined in this structure at non-tiny configuration (FF_FS_TINY == 0), so that the FIL structures at that configuration should not be defined as auto variable.
typedef struct { FFOBJID obj; /* Object identifier */ BYTE flag; /* File object status flags */ BYTE err; /* Abort flag (error code) */ FSIZE_t fptr; /* File read/write pointer (Byte offset origin from top of the file) */ DWORD clust; /* Current cluster of fptr (One cluster behind if fptr is on the cluster boundary. Invalid if fptr == 0.) */ LBA_t sect; /* Current data sector (Can be invalid if fptr is on the cluster boundary.)*/ #if !FF_FS_READONLY LBA_t dir_sect; /* Sector number containing the directory entry */ BYTE* dir_ptr; /* Ponter to the directory entry in the window */ #endif #if FF_USE_FASTSEEK DWORD* cltbl; /* Pointer to the cluster link map table (Nulled on file open. Set by application.) */ #endif #if !FF_FS_TINY BYTE buf[FF_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;