FSEEK(3) BSD Library Functions Manual FSEEK(3)NAME
fgetpos, fseek, fseeko, fsetpos, ftell, ftello, rewind — reposition a
Standard C Library (libc, -lc)
fseek(FILE *stream, long offset, int whence);
fgetpos(FILE * restrict stream, fpos_t * restrict pos);
fsetpos(FILE *stream, const fpos_t *pos);
fseeko(FILE *stream, off_t offset, int whence);
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)
and ungetwc(3) functions on the same stream.
The ftell() function obtains the current value of the file position indi‐
cator 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
Since rewind() does not return a value, an application wishing to detect
errors should clear errno, then call rewind(), and if errno is non-zero,
assume an error has occurred.
The fseeko() function is identical to fseek(), except it takes an off_t
argument instead of a long. Likewise, the ftello() function is identical
to ftell(), except it returns an off_t.
The fgetpos() and fsetpos() functions are alternate interfaces for
retrieving and setting the current position in the file, similar to
ftell() and fseek(), except that the current position is stored in an
opaque object of type fpos_t pointed to by pos. These functions provide
a portable way to seek to offsets larger than those that can be repre‐
sented by a long int. They may also store additional state information
in the fpos_t object to facilitate seeking within files containing multi‐
byte characters with state-dependent encodings. Although fpos_t has tra‐
ditionally been an integral type, applications cannot assume that it is;
in particular, they must not perform arithmetic on objects of this type.
If the stream is a wide character stream (see fwide(3)), the position
specified by the combination of offset and whence must contain the first
byte of a multibyte sequence.
The rewind() function returns no value.
The fgetpos(), fseek(), fseeko(), and fsetpos() functions return the
value 0 if successful; otherwise the value -1 is returned and the global
variable errno is set to indicate the error.
Upon successful completion, ftell() and ftello() return the current off‐
set. Otherwise, -1 is returned and the global variable errno is set to
indicate the error.
[EBADF] The stream argument is not a seekable stream.
[EINVAL] The whence argument is invalid or the resulting file-
position indicator would be set to a negative value.
[EOVERFLOW] The resulting file offset would be a value which can‐
not be represented correctly in an object of type
off_t for fseeko() and ftello() or long for fseek()
[ESPIPE] The file descriptor underlying stream is associated
with a pipe or FIFO or file-position indicator value
is unspecified (see ungetc(3)).
The functions 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).
SEE ALSOlseek(2), clearerr(3), fwide(3), ungetc(3), ungetwc(3)STANDARDS
The fgetpos(), fsetpos(), fseek(), ftell(), and rewind() functions con‐
form to ISO/IEC 9899:1990 (“ISO C90”).
The fseeko() and ftello() functions conform to IEEE Std 1003.1-2001
BSD March 19, 2004 BSD