#include <sys/types.h> #include <unistd.h>
off_t lseek (
int whence );
Interfaces documented on this reference page conform to industry standards as follows:
lseek(): POSIX.1, XPG4
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 parameter.
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, 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.
Functions: fcntl(2), fseek(3), open(2), read(2), write(2)
Standards: standards(5) delim off