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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | STANDARDS | HISTORY | SEE ALSO | COLOPHON |
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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 stream.
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 semantics.
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.
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).
For an explanation of the terms used in this section, see
attributes(7).
┌─────────────────────────────────────┬───────────────┬─────────┐
│ Interface │ Attribute │ Value │
├─────────────────────────────────────┼───────────────┼─────────┤
│ fseek(), ftell(), rewind(), │ Thread safety │ MT-Safe │
│ fgetpos(), fsetpos() │ │ │
└─────────────────────────────────────┴───────────────┴─────────┘
C11, POSIX.1-2008.
POSIX.1-2001, C89.
lseek(2), fseeko(3)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.9.1.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2024-06-26. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
man-pages@man7.org
Linux man-pages 6.9.1 2024-05-02 fseek(3)
Pages that refer to this page: lseek(2), fgetc(3), fmemopen(3), fopen(3), fopencookie(3), fseeko(3), gets(3), open_memstream(3), puts(3), stdio(3), feature_test_macros(7)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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