libc.info: fgetpos

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`fgetpos'--record position in a stream or file

*Synopsis*
     #include <stdio.h>
     int fgetpos(FILE *FP, fpos_t *POS);
   *Description*
Objects of type `FILE' can have a "position" that records how much of
the file your program has already read.  Many of the `stdio' functions
depend on this position, and many change it as a side effect.
   You can use `fgetpos' to report on the current position for a file
identified by FP; `fgetpos' will write a value representing that
position at `*POS'.  Later, you can use this value with `fsetpos' to
return the file to this position.
   In the current implementation, `fgetpos' simply uses a character
count to represent the file position; this is the same number that
would be returned by `ftell'.
*Returns*
`fgetpos' returns `0' when successful.  If `fgetpos' fails, the result
is `1'.  Failure occurs on streams that do not support positioning; the
global `errno' indicates this condition with the value `ESPIPE'.
*Portability*
`fgetpos' is required by the ANSI C standard, but the meaning of the
value it records is not specified beyond requiring that it be
acceptable as an argument to `fsetpos'.  In particular, other
conforming C implementations may return a different result from `ftell'
than what `fgetpos' writes at `*POS'.
   No supporting OS subroutines are required.