Standard C Library Functions fseek(3C)
NAME
fseek, fseeko - reposition a file-position indicator in a
streamSYNOPSIS
#include
int fseek(FILE *stream, long offset, int whence);int fseeko(FILE *stream, off_t offset, int whence);
DESCRIPTION
The fseek() function sets the file-position indicator for
the stream pointed to by stream. The fseeko() function is
identical to fseek() except for the type of offset. The new position, measured in bytes from the beginning of the file, is obtained by adding offset to the position specified by whence, whose values are defined inas follows: SEEK_SET Set position equal to offset bytes.
SEEK_CUR Set position to current location plus offset.
SEEK_END Set position to EOF plus offset.
If the stream is to be used with wide character input/output functions, offset must either be 0 or a value returned by an earlier call to ftell(3C) on the same stream and whence mustbe SEEK_SET.
A successful call to fseek() clears the end-of-file indica-
tor for the stream and undoes any effects of ungetc(3C) and ungetwc(3C) on the same stream. After an fseek() call, the next operation on an update stream may be either input or output. If the most recent operation, other than ftell(3C), on agiven stream is fflush(3C), the file offset in the underly-
ing open file description will be adjusted to reflect the location specified by fseek().SunOS 5.11 Last change: 1 Nov 2003 1
Standard C Library Functions fseek(3C)The fseek() function allows the file-position indicator to
be set beyond the end of existing data in the file. If data is later written at this point, subsequent reads of data in the gap will return bytes with the value 0 until data is actually written into the gap. The value of the file offset returned by fseek() on devices which are incapable of seeking is undefined. If the stream is writable and buffered data had not been written to the underlying file, fseek() will cause the unwritten data to be written to the file and mark thest_ctime and st_mtime fields of the file for update.
RETURN VALUES
The fseek() and fseeko() functions return 0 on success; oth-
erwise, they returned -1 and set errno to indicate the
error.ERRORS
The fseek() and fseeko() functions will fail if, either the
stream is unbuffered or the stream's buffer needed to beflushed, and the call to fseek() or fseeko() causes an
underlying lseek(2) or write(2) to be invoked:EAGAIN The O_NONBLOCK flag is set for the file descriptor
and the process would be delayed in the write operation. EBADF The file descriptor underlying the stream file is not open for writing or the stream's buffer needed to be flushed and the file is not open. EFBIG An attempt was made to write a file that exceeds the maximum file size or the process's file size limit, or the file is a regular file and an attempt was made to write at or beyond the offset maximum associated with the corresponding stream. EINTR The write operation was terminated due to the receipt of a signal, and no data was transferred. EINVAL The whence argument is invalid. The resultingfile-position indicator would be set to a negative
value.SunOS 5.11 Last change: 1 Nov 2003 2
Standard C Library Functions fseek(3C)EIO A physical I/O error has occurred; or the process
is a member of a background process group attempt-
ing to perform a write(2) operation to its con-
trolling terminal, TOSTOP is set, the process is neither ignoring nor blocking SIGTTOU, and the process group of the process is orphaned. ENOSPC There was no free space remaining on the device containing the file.ENXIO A request was made of a non-existent device, or
the request was outside the capabilities of the device.EPIPE The file descriptor underlying stream is associ-
ated with a pipe or FIFO. EPIPE An attempt was made to write to a pipe or FIFO that is not open for reading by any process. A SIGPIPE signal will also be sent to the calling thread. The fseek() function will fail if: EOVERFLOW The resulting file offset would be a value which cannot be represented correctly in an object of type long.The fseeko() function will fail if:
EOVERFLOW The resulting file offset would be a value which cannot be represented correctly in anobject of type off_t.
USAGE
Although on the UNIX system an offset returned by ftell() or ftello() (see ftell(3C)) 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 fseek() directly. Arithmetic may not meaningfully be performed on such an offset, which is not necessarily measured in bytes.SunOS 5.11 Last change: 1 Nov 2003 3
Standard C Library Functions fseek(3C)The fseeko() function has a transitional interface for 64-
bit file offsets. See lf64(5).ATTRIBUTES
See attributes(5) for descriptions of the following attri-
butes:____________________________________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|_____________________________|_____________________________|
| Interface Stability | Committed ||_____________________________|_____________________________|
| MT-Level | MT-Safe |
|_____________________________|_____________________________|
| Standard | See standards(5). ||_____________________________|_____________________________|
SEE ALSO
getrlimit(2), ulimit(2), ftell(3C), rewind(3C), ungetc(3C), ungetwc(3C), attributes(5), lf64(5), standards(5)SunOS 5.11 Last change: 1 Nov 2003 4