NAME

lseek, tell − move read/write pointer

SYNOPSIS

long lseek(fildes, offset, whence)
int fildes;
long offset;
int whence;

long tell(fildes)
int fildes;

DESCRIPTION

The file descriptor refers to a file open for reading or writing.  The read (resp. write) pointer for the file is set as follows:

If whence is 0, the pointer is set to offset bytes. 

If whence is 1, the pointer is set to its current location plus offset.

If whence is 2, the pointer is set to the size of the file plus offset.

The returned value is the resulting pointer location. 

The function tell(fildes) is identical to lseek(fildes, 0L, 1).

Seeking far beyond the end of a file, then writing, creates a gap or ’hole’, which occupies no physical space and reads as zeros. 

SEE ALSO

open(2), creat(2), fseek(3)

DIAGNOSTICS

−1 is returned for an undefined file descriptor, seek on a pipe, or seek to a position before the beginning of file. 

BUGS

Lseek is a no-op on character special files. 

7th Edition