lseek - Move read-write file offset
#include <sys/types.h> #include <unistd.h>
int whence );
Interfaces documented on this reference page conform to
industry standards as follows:
lseek(): XSH4.0, XSH4.2, XSH5.0, XNS4.0, XNS5.0
Refer to the standards(5) reference page for more information
about industry standards and associated tags.
Specifies a file descriptor obtained from a successful
open() or fcntl() function. Specifies a value, in bytes,
that is used in conjunction with the whence parameter to
set the file pointer. A negative value causes seeking in
the reverse direction. The resulting file position may
also be negative. Specifies how to interpret the offset
parameter in setting the file pointer associated with the
filedes parameter. Values for the whence parameter are:
Sets the file pointer to the value of the offset parameter.
Sets the file pointer to its current location plus
the value of the offset parameter. Sets the file pointer
to the size of the file plus the value of the offset
The lseek() function sets the file offset for the open
file specified by the filedes parameter. The whence parameter
determines how the offset is to be interpreted.
The lseek() function allows the file offset to be set
beyond the end of existing data in the file. If data is
later written at this point, subsequently reading data in
the gap returns bytes with the value 0 (zero) until data
is actually written into the gap.
By itself, the lseek() function does not extend the size
of the file.
Upon successful completion, the resulting pointer location
(the file offset), measured in bytes from the beginning of
the file, is returned. If the lseek() function fails, the
file offset remains unchanged, a value of (off_t) - 1 is
returned, and errno is set to indicate the error.
If the lseek() function fails, the file offset remains
unchanged and errno may be set to one of the following
values: The filedes parameter is not an open file descriptor.
The whence parameter is an invalid value or the
resulting file offset would be invalid. The filedes
parameter is associated with a pipe (FIFO), a socket, or a
multiplexed special file.
The filedes parameter underlying the stream is
associated with a socket.
Functions: fcntl(2), fseek(3), open(2), read(2), write(2)
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