fseek(3)                                              Library Functions Manual                                             fseek(3)

       fgetpos, fseek, fsetpos, ftell, rewind - reposition a stream

       Standard C library (libc, -lc)

       #include <stdio.h>

       int fseek(FILE *stream, long offset, int whence);
       long ftell(FILE *stream);

       void rewind(FILE *stream);

       int fgetpos(FILE *restrict stream, fpos_t *restrict pos);
       int fsetpos(FILE *stream, const fpos_t *pos);

       The  fseek()  function  sets the file position indicator for the stream pointed to by stream.  The new position, measured in
       bytes, is obtained by adding offset bytes to the position specified by whence.  If whence is set to SEEK_SET,  SEEK_CUR,  or
       SEEK_END,  the offset is relative to the start of the file, the current position indicator, or end-of-file, respectively.  A
       successful call to the fseek() function clears the end-of-file indicator for the  stream  and  undoes  any  effects  of  the
       ungetc(3) function on the same stream.

       The ftell() function obtains the current value of the file position indicator for the stream pointed to by stream.

       The rewind() function sets the file position indicator for the stream pointed to by stream to the beginning of the file.  It
       is equivalent to:

              (void) fseek(stream, 0L, SEEK_SET)

       except that the error indicator for the stream is also cleared (see clearerr(3)).

       The fgetpos() and fsetpos() functions are alternate interfaces equivalent  to  ftell()  and  fseek()  (with  whence  set  to
       SEEK_SET), setting and storing the current value of the file offset into or from the object referenced by pos.  On some non-
       UNIX systems, an fpos_t object may be a complex object and these routines may be the only way to portably reposition a  text

       If  the  stream  refers  to a regular file and the resulting stream offset is beyond the size of the file, subsequent writes
       will extend the file with a hole, up to the offset, before committing any data.  See lseek(2) for details  on  file  seeking

       The rewind() function returns no value.  Upon successful completion, fgetpos(), fseek(), fsetpos() return 0, and ftell() re‐
       turns the current offset.  Otherwise, -1 is returned and errno is set to indicate the error.

       EINVAL The whence argument to fseek() was not SEEK_SET, SEEK_END, or SEEK_CUR.  Or: the resulting file offset would be nega‐

       ESPIPE The file descriptor underlying stream is not seekable (e.g., it refers to a pipe, FIFO, or socket).

       The functions fgetpos(), fseek(), fsetpos(), and ftell() may also fail and set errno for any of the errors specified for the
       routines fflush(3), fstat(2), lseek(2), and malloc(3).

       For an explanation of the terms used in this section, see attributes(7).

       │Interface                                                                                        │ Attribute     │ Value   │
       │fseek(), ftell(), rewind(), fgetpos(), fsetpos()                                                 │ Thread safety │ MT-Safe │

       POSIX.1-2001, POSIX.1-2008, C99.

       lseek(2), fseeko(3)

Linux man-pages 6.03                                         2022-12-29                                                    fseek(3)