#include <sys/types.h> #include <unistd.h>offset_t llseek(int fildes, offset_t offset, int whence);
The llseek() function sets the 64-bit extended file pointer associated with the open file descriptor specified by fildes as follows:
If whence is SEEK_SET, the pointer is set to offset bytes.
If whence is SEEK_CUR, the pointer is set to its current location plus offset.
If whence is SEEK_END, the pointer is set to the size of the file plus offset.
Although each file has a 64-bit file pointer associated with it, some existing file system types (such as tmpfs) do not support the full range of 64-bit offsets. In particular, on such file systems, non-device files remain limited to offsets of less than two gigabytes. Device drivers may support offsets of up to 1024 gigabytes for device special files.
Some devices are incapable of seeking. The value of the file pointer associated with such a device is undefined.
Upon successful completion, llseek() returns the resulting pointer location as measured in bytes from the beginning of the file. Remote file descriptors are the only ones that allow negative file pointers. Otherwise, -1 is returned, the file pointer remains unchanged, and errno is set to indicate the error.
The llseek() function will fail if:
The fildes argument is not an open file descriptor.
The whence argument is not SEEK_SET, SEEK_CUR, or SEEK_END; the offset argument is not a valid offset for this file system type; or the fildes argument is not a remote file descriptor and the resulting file pointer would be negative.
The fildes argument is associated with a pipe or FIFO.