fseek(3) - f37

1FSEEK(3)                   Linux Programmer's Manual                  FSEEK(3)
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NAME

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

9       #include <stdio.h>
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11       int fseek(FILE *stream, long offset, int whence);
12       long ftell(FILE *stream);
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14       void rewind(FILE *stream);
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16       int fgetpos(FILE *restrict stream, fpos_t *restrict pos);
17       int fsetpos(FILE *stream, const fpos_t *pos);
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DESCRIPTION

20       The  fseek()  function  sets the file position indicator for the stream
21       pointed to by stream.  The new position, measured in bytes, is obtained
22       by  adding offset bytes to the position specified by whence.  If whence
23       is set to SEEK_SET, SEEK_CUR, or SEEK_END, the offset  is  relative  to
24       the  start of the file, the current position indicator, or end-of-file,
25       respectively.  A successful call to the  fseek()  function  clears  the
26       end-of-file  indicator  for  the  stream  and undoes any effects of the
27       ungetc(3) function on the same stream.
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29       The ftell() function obtains the current value of the file position in‐
30       dicator for the stream pointed to by stream.
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32       The  rewind()  function sets the file position indicator for the stream
33       pointed to by stream to the beginning of the file.   It  is  equivalent
34       to:
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36              (void) fseek(stream, 0L, SEEK_SET)
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38       except  that  the  error  indicator for the stream is also cleared (see
39       clearerr(3)).
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41       The fgetpos() and fsetpos() functions are alternate interfaces  equiva‐
42       lent  to ftell() and fseek() (with whence set to SEEK_SET), setting and
43       storing the current value of the file offset into or  from  the  object
44       referenced by pos.  On some non-UNIX systems, an fpos_t object may be a
45       complex object and these routines may be the only way to portably repo‐
46       sition a text stream.
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RETURN VALUE

49       The  rewind()  function  returns no value.  Upon successful completion,
50       fgetpos(), fseek(), fsetpos() return 0, and ftell() returns the current
51       offset.  Otherwise, -1 is returned and errno is set to indicate the er‐
52       ror.
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ERRORS

55       EINVAL The whence argument to fseek() was not  SEEK_SET,  SEEK_END,  or
56              SEEK_CUR.  Or: the resulting file offset would be negative.
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58       ESPIPE The  file descriptor underlying stream is not seekable (e.g., it
59              refers to a pipe, FIFO, or socket).
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61       The functions fgetpos(), fseek(), fsetpos(), and ftell() may also  fail
62       and  set  errno  for  any  of  the  errors  specified  for the routines
63       fflush(3), fstat(2), lseek(2), and malloc(3).
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ATTRIBUTES

66       For an  explanation  of  the  terms  used  in  this  section,  see  at‐
67       tributes(7).
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69       ┌────────────────────────────────────────────┬───────────────┬─────────┐
70       │Interface                                   │ Attribute     │ Value   │
71       ├────────────────────────────────────────────┼───────────────┼─────────┤
72       │fseek(), ftell(), rewind(), fgetpos(),      │ Thread safety │ MT-Safe │
73       │fsetpos()                                   │               │         │
74       └────────────────────────────────────────────┴───────────────┴─────────┘
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CONFORMING TO

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

83       This page is part of release 5.13 of the Linux  man-pages  project.   A
84       description  of  the project, information about reporting bugs, and the
85       latest    version    of    this    page,    can     be     found     at
86       https://www.kernel.org/doc/man-pages/.
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90GNU                               2021-03-22                          FSEEK(3)