LSEEK

Section: System Calls (2)
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BSD mandoc
BSD 4

NAME

lseek - reposition read/write file offset

SYNOPSIS

Fd #include <unistd.h> Ft off_t Fn lseek int fildes off_t offset int whence

DESCRIPTION

The Fn lseek function repositions the offset of the file descriptor Fa fildes to the argument Fa offset according to the directive Fa whence. The argument Fa fildes must be an open file descriptor. Fn Lseek repositions the file pointer Fa fildes as follows:

If: Fa whence is SEEK_SET the offset is set to Fa offset bytes.
If: Fa whence is SEEK_CUR the offset is set to its current location plus Fa offset bytes.
If: Fa whence is SEEK_END the offset is set to the size of the file plus Fa offset bytes.

The Fn lseek function allows the file offset to be set beyond the end of the existing end-of-file of the file. If data is later written at this point, subsequent reads of the data in the gap return bytes of zeros (until data is actually written into the gap).

Some devices are incapable of seeking. The value of the pointer associated with such a device is undefined.

RETURN VALUES

Upon successful completion, Fn lseek returns the resulting offset location as measured in bytes from the beginning of the file. Otherwise, a value of -1 is returned and errno is set to indicate the error.

ERRORS

Fn Lseek will fail and the file pointer will remain unchanged if:

Bq Er EBADF: Fildes is not an open file descriptor.
Bq Er ESPIPE: Fildes is associated with a pipe, socket, or FIFO.
Bq Er EINVAL: Fa Whence is not a proper value.

BUGS

This document's use of Fa whence is incorrect English, but is maintained for historical reasons.

STANDARDS

The Fn lseek function conforms to St -p1003.1-88 .

This document was created by man2html, using the manual pages.
Time: 16:28:59 GMT, April 18, 2022