What's the difference between fgetpos/fsetpos
What are fgetpos and fsetpos good for?
A: ftell and fseek use type long int to represent offsets (positions) in a file, and may therefore be limited to offsets which can be represented in a long int. (Type long int is not guaranteed to hold values larger than 2**31-1, limiting the maximum offset to 2 gigabytes). The newer fgetpos and fsetpos functions, on the other hand, use a special typedef, fpos_t, to represent the offsets. The type behind this typedef, if chosen appropriately, can represent arbitrarily large offsets, so fgetpos and fsetpos can be used with arbitrarily huge files. fgetpos and fsetpos also record the state associated with multibyte streams. See also question 1.4.
K&R2 Sec. B1.6 p. 248
ISO Sec. 7.9.1, Secs. 18.104.22.168,22.214.171.124
H&S Sec. 15.5 p. 252