Linux and UNIX Man Pages

Linux & Unix Commands - Search Man Pages

lseek(2) [ultrix man page]

lseek(2)							System Calls Manual							  lseek(2)

Name
       lseek, tell - move read or write pointer

Syntax
       #include <sys/types.h>
       #include <unistd.h>

       pos = lseek(d, offset, whence)
       off_t pos;
       int d, whence;
       off_t offset;

       pos = tell(d)
       off_t pos;
       int d;

Description
       The system call moves the file pointer associated with a file or device open for reading or writing.

       The descriptor d refers to a file or device open for reading or writing.  The system call sets the file pointer of d as follows:

       o    If whence is SEEK_SET, the pointer is set to offset bytes.

       o    If whence is SEEK_CUR the pointer is set to its current location plus offset.

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

       Seeking beyond the end of a file and then writing to the file creates a gap or hole that does not occupy physical space and reads as zeros.

       The system call returns the offset of the current byte relative to the beginning of the file associated with the file descriptor.

Environment
   System Five
       If  you	compile  a  program  in  the System Five environment, an invalid whence argument causes SIGSYS to be sent.  This complies with the
       behavior described in the System V Interface Definition (SVID), Issue 1.

Return Values
       Upon successful completion, a long integer (the current file pointer value) is returned.  This pointer is measured in bytes from the begin-
       ning  of  the file, where the first byte is byte 0.  (Note that some devices are incapable of seeking.  The value of the pointer associated
       with such a device is undefined.)  If a value of -1 is returned, errno is set to indicate the error.

Diagnostics
       The system call fails and the file pointer remains unchanged under the following conditions:

       [EBADF]	      The fildes is not an open file descriptor.

       [EINVAL]       The whence is not a proper value.

       [ESPIPE]       The fildes is associated with a pipe or a socket.

See Also
       dup(2), open(2)

																	  lseek(2)

Check Out this Related Man Page

LSEEK(2)							System Calls Manual							  LSEEK(2)

NAME
lseek - move read/write pointer SYNOPSIS
#include <sys/file.h> #define L_SET 0 /* set the seek pointer */ #define L_INCR 1 /* increment the seek pointer */ #define L_XTND 2 /* extend the file size */ pos = lseek(d, offset, whence) off_t pos; int d; off_t offset; int whence; DESCRIPTION
The descriptor d refers to a file or device open for reading and/or writing. Lseek sets the file pointer of d as follows: If whence is L_SET, the pointer is set to offset bytes. If whence is L_INCR, the pointer is set to its current location plus offset. If whence is L_XTND, the pointer is set to the size of the file plus offset. Upon successful completion, the resulting pointer location as measured in bytes from beginning of the file is returned. Some devices are incapable of seeking. The value of the pointer associated with such a device is undefined. NOTES
Seeking far beyond the end of a file, then writing, creates a gap or "hole", which occupies no physical space and reads as zeros. RETURN VALUE
Upon successful completion, the current file pointer value is returned. Otherwise, a value of -1 is returned and errno is set to indicate the error. ERRORS
Lseek will fail and the file pointer will remain unchanged if: [EBADF] Fildes is not an open file descriptor. [ESPIPE] Fildes is associated with a pipe or a socket. [EINVAL] Whence is not a proper value. SEE ALSO
dup(2), open(2) BUGS
This document's use of whence is incorrect English, but maintained for historical reasons. 4th Berkeley Distribution February 24, 1986 LSEEK(2)
Man Page