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FSEEK(3) Linux Programmer's Manual FSEEK(3)
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 po‐
sition 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)
GNU 2021-03-22 FSEEK(3)