C Standard Library: File Positioning Functions

1.6 File Positioning Functions
int fseek(FILE *stream, long offset, int origin)
fseek sets the file position for stream; a subsequent read or write will access data
beginning at the new position. For a binary file, the position is set to offset characters
from origin, which may be SEEK_SET (beginning), SEEK_CUR (current position), or
SEEK_END (end of file). For a text stream, offset must be zero, or a value returned by
ftell (in which case origin must be SEEK_SET). fseek returns non-zero on error.

long ftell(FILE *stream)
ftell returns the current file position for stream, or -1 on error.

void rewind(FILE *stream)
rewind(fp) is equivalent to fseek(fp, 0L, SEEK_SET); clearerr(fp).

int fgetpos(FILE *stream, fpos_t *ptr)
fgetpos records the current position in stream in *ptr, for subsequent use by
fsetpos. The type fpos_t is suitable for recording such values. fgetpos returns nonzero
on error.

int fsetpos(FILE *stream, const fpos_t *ptr)

fsetpos positions stream at the position recorded by fgetpos in *ptr. fsetpos
returns non-zero on error.