fseeko, fseeko64, ftello, ftello64 --
reposition a file pointer in a stream
int fseeko(FILE stream, off_t offset, int ptrname);
int fseeko64(FILE stream, off64_t offset, int ptrname);
off_t ftello(FILE stream);
off64_t ftello64(FILE stream);
fseeko sets the position of the next input or output operation on the
The new position is at the signed distance
bytes from the beginning, from the current position, or from the end of
the file, according to a
value of SEEK_SET, SEEK_CUR, or
SEEK_END (defined in stdio.h) as follows:
set position equal to offset bytes.
set position to current location plus offset.
set position to EOF plus offset.
fseeko allows the file position indicator to be set
beyond the end of the existing data in the file.
If data is later written at this point, subsequent reads of data in
the gap will return zero until data is actually written into the gap.
fseeko, by itself, does not extend the size of the file.
fseek clears the EOF indicator and undoes any effects
of ungetc on stream.
After fseek, the next operation on a file opened for update
may be either input or output.
If stream is writable and buffered data has not been written to the
underlying file, fseek causes the unwritten data to
be written to the file.
ftello returns the offset of the current byte relative to the beginning
of the file associated with the named
fseeko and fseeko64 return -1 for improper seeks,
An improper seek can be, for example, an fseeko
or an fseeko64 done on a file that has not been
opened via fopen or fopen64; in particular,
fseeko and fseeko64 may not be used on a
terminal or on a file opened via popen.
After a stream is closed, no further operations are defined on that stream.
fseeko and ftello fail when
the resulting file offset would be a value which cannot be represented
correctly in an object of type off_t.
Although on the
system an offset returned by ftello is measured in bytes, and it is
permissible to seek to positions relative to that offset,
portability to non-UNIX systems requires that
an offset be used by fseeko directly.
Arithmetic may not meaningfully be performed on such
an offset, which is not necessarily measured in bytes.
Considerations for large file support
fseeko64 and ftello64 support large files, but are otherwise identical
and ftello, respectively.
For details on programming for large file capable applications, see
``Large File Support''
© 2004 The SCO Group, Inc. All rights reserved.
UnixWare 7 Release 7.1.4 - 25 April 2004