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Technical Reference: Base Operating System and Extensions, Volume 1

lseek, llseek or lseek64 Subroutine


Moves the read-write file pointer.


Standard C Library (libc.a)


off_t lseek ( FileDescriptor, Offset, Whence)
int FileDescriptorWhence;
off_t Offset;

offset_t llseek (FileDescriptor, Offset, Whence)
int FileDescriptorWhence;
offset_t Offset;

off64_t lseek64 (FileDescriptor, Offset, Whence)
int FileDescriptor, Whence;
off64_t Offset;


The lseek, llseek, and lseek64 subroutines set the read-write file pointer for the open file specified by the FileDescriptor parameter. The lseek subroutine limits the Offset to OFF_MAX.

In the large file enabled programming environment, lseek subroutine is redefined to lseek64.


FileDescriptor Specifies a file descriptor obtained from a successful open or fcntl subroutine.
Offset 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.
Whence Specifies how to interpret the Offset parameter by setting the file pointer associated with the FileDescriptor parameter to one of the following variables:
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.

Return Values

Upon successful completion, the resulting pointer location, measured in bytes from the beginning of the file, is returned. If either the lseek or llseek subroutines are unsuccessful, a value of -1 is returned and the errno global variable is set to indicate the error.

Error Codes

The lseek or llseek subroutines are unsuccessful and the file pointer remains unchanged if any of the following are true:

EBADF The FileDescriptor parameter is not an open file descriptor.
ESPIPE The FileDescriptor parameter is associated with a pipe (FIFO) or a socket.
EINVAL The resulting offset would be greater than the maximum offset allowed for the file or device associated with FileDescriptor.
EOVERFLOW The resulting offset is larger than can be returned properly.


/usr/include/unistd.h Defines standard macros, data types and subroutines.

Related Information

The fcntl (fcntl, dup, or dup2 Subroutine) subroutine, fseek, rewind, ftell, fgetpos, or fsetpos (fseek, fseeko, fseeko64, rewind, ftell, ftello, ftello64, fgetpos, fgetpos64, fsetpos, or fsetpos64 Subroutine) subroutine, open, openx, or creat (open, openx, open64, creat, or creat64 Subroutine) subroutine, read, readx, readv, or readvx subroutine, write, writex, writev, or writevx subroutine.

File Systems and Directories in AIX 5L Version 5.2 General Programming Concepts: Writing and Debugging Programs.

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