FSEEK(3) BSD Library Functions Manual FSEEK(3)
NAME
fgetpos, fseek, fseeko, fsetpos, ftell, ftello, rewind -- reposition a stream
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <stdio.h>
int
fgetpos(FILE *restrict stream, fpos_t *restrict pos);
int
fseek(FILE *stream, long offset, int whence);
int
fseeko(FILE *stream, off_t offset, int whence);
int
fsetpos(FILE *stream, const fpos_t *pos);
long
ftell(FILE *stream);
off_t
ftello(FILE *stream);
void
rewind(FILE *stream);
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 position indicator, or end-of-file, respectively. A successful call to the fseek() func-tion function
tion 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 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)).
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 off-sets offsets
sets larger than those that can be represented by a long int. They may also store additional state
information in the fpos_t object to facilitate seeking within files containing multibyte characters
with state-dependent encodings. Although fpos_t has traditionally 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.
RETURN VALUES
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 offset. Otherwise, -1 is returned
and the global variable errno is set to indicate the error.
ERRORS
[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 cannot be represented correctly in
an object of type off_t for fseeko() and ftello() or long for fseek() and ftell().
[ESPIPE] The file descriptor underlying stream is associated with a pipe or FIFO or file-position fileposition
position indicator value is unspecified (see ungetc(3)).
The functions fgetpos(), fseek(), fseeko(), fsetpos(), ftell(), and ftello() may also fail and set
errno for any of the errors specified for the routines fflush(3), fstat(2), lseek(2), and malloc(3).
LEGACY SYNOPSIS
#include <stdio.h>
#include <sys/types.h>
int
fseeko(FILE *stream, off_t offset, int whence);
The include file <sys/types.h> supplies the definition for off_t.
SEE ALSO
lseek(2), clearerr(3), fwide(3), ungetc(3), ungetwc(3), compat(5)
STANDARDS
The fgetpos(), fsetpos(), fseek(), ftell(), and rewind() functions conform to ISO/IEC 9899:1990
(``ISO C90'').
The fseeko() and ftello() functions conform to IEEE Std 1003.1-2001 (``POSIX.1'').
BSD March 19, 2004 BSD
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