FAT File Systems - USB Mass Storage: Designing and Programming Devices and Embedded Hosts - page 191

File Information

A FILE structure can store information about a file, including its location in
a volume and a location currently being accessed in the file. (Chapter 9 has
more about directories, and Chapter 10 has more about accessing files.)
// A short file name has 11 or fewer characters, not counting the dot.

#define FILE_NAME_SIZE 11

typedef struct
{
unsigned write :1; // Set if the file was opened for writing.
unsigned FileWriteEOF :1; // Set if writing and have reached the end of the file.
}FileFlags;

typedef struct
{
DISK *dsk; // a DISK structure for the volume containing the file

word cluster; // number of the first file's cluster

word ccls; // current cluster

word sec; // current sector in the current cluster

word pos; // current byte location in the current sector

dword seek; // current byte location in the file

dword size; // file size

FileFlags Flags; // write mode and end-of-file indicators

word time; // last update time

word date; // last update date

char name[FILE_NAME_SIZE]; // file name

word entry; // position of the file's entry in its directory

word chk; // FILE structure checksum = ~( entry + name[0])

word attributes; // file's attributes

word dirclus; // first cluster of the file's directory

word dirccls; // current cluster of the file's directory

} FILE;
A FILEOBJ is a pointer to a FILE structure:
typedef FILE * FILEOBJ;
Functions in this chapter use these defines:
#define CLUSTER_FAIL 0xffff
#define LAST_CLUSTER 0xfff8
#define LAST_CLUSTER_FAT16 0xfff8