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FSEEK(3) NetBSD Library Functions Manual FSEEK(3)
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Maintained for NetBSD
by Kimmo Suominen.
Based on man-cgi by Panagiotis Christias.
fgetpos, fseek, fseeko, fsetpos, ftell, ftello, rewind -- reposition a
Standard C Library (libc, -lc)
fseek(FILE *stream, long int offset, int whence);
fseeko(FILE *stream, off_t offset, int whence);
fgetpos(FILE * restrict stream, fpos_t * restrict pos);
fsetpos(FILE * restrict stream, const fpos_t * restrict 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 fseeko() function is identical to the fseek() function except that
the offset argument is of type off_t.
The ftell() function obtains the current value of the file position indi-
cator for the stream pointed to by stream.
The ftello() function is identical to the ftell() function except that
the return value is of type off_t.
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
In this implementations, ``fpos_t'' is a complex object that represents
both the position and the parse state of the stream, making these rou-
tines the only way to portably reposition a text stream. The pos argu-
ment of fsetpos() must always be initialized by a call to fgetpos().
The rewind() function returns no value.
Upon successful completion, fgetpos(), fseek(), fseeko(), and fsetpos()
return 0, whereas the functions ftell() and ftello() return the current
offset. On failure, fseek(), fseeko(), ftell(), and ftello() return -1,
while fgetpos() and fsetpos() return a nonzero value.
On error all functions set the global variable errno to indicate the
error. Since the rewind() function does not return an error code, appli-
cations need to clear errno before calling it in order to detect errors.
[EBADF] The stream specified is not a seekable stream.
[EINVAL] The whence argument to fseek() was not SEEK_SET,
SEEK_END, or SEEK_CUR.
[EOVERFLOW] For ftell(), the current file offset cannot be repre-
sented correctly in an object of type long.
The function fgetpos(), fseek(), fseeko(), fsetpos(), ftell(), ftello(),
and rewind() may also fail and set errno for any of the errors specified
for the routines fflush(3), fstat(2), lseek(2), and malloc(3).
lseek(2), clearerr(3), ungetc(3)
The fgetpos(), fsetpos(), fseek(), ftell(), and rewind() functions con-
form to ANSI X3.159-1989 (``ANSI C89''). The fseeko() and ftello() func-
tions conform to X/Open System Interfaces and Headers Issue 5 (``XSH5'').
The fgetpos() and fsetpos() functions don't store/set shift states of the
stream in this implementation.
NetBSD 9.99 September 11, 2021 NetBSD 9.99