Manpages - fseek.3

Table of Contents

NAME

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

SYNOPSIS

  #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);

DESCRIPTION

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 stream.

RETURN VALUE

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

ERRORS

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

ATTRIBUTES

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

CONFORMING TO

POSIX.1-2001, POSIX.1-2008, C89, C99.

SEE ALSO

*lseek*(2), *fseeko*(3)

COLOPHON

This page is part of release 5.13 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.

Author: dt

Created: 2022-02-20 Sun 15:39