pread64

Reads data from a file.

Library:LibC
Classification:POSIX
Service:File and Directory I/O

Syntax

  #include <unistd.h> 
   
  ssize_t  pread64 (
     int        fildes,
     void      *buf,
     size_t     nbytes,
     off64_t    off);

Parameters

fildes

(IN) Specifies a file descriptor.

buf

(OUT) Points to a buffer to receive the data.

nbytes

(IN) Specifies the number of bytes to read.

off

(IN) Specifies the starting offset in the file for the read.

Return Values

If successful, returns the number of bytes of data transmitted from the file to the buffer. Normally, this is the number given by the nbytes parameter. When the end-of-file is encountered before the read completes, the return value is less than the number of bytes requested.

If nbytes is 0, returns 0 and may set errno to one of the following. If unsuccessful, returns a -1 and sets errno to one of the following:

Decimal

Constant

Description

4

EBADF

Invalid file descriptor.

5

ENOMEM

Insufficient memory.

9

EINVAL

The offset parameter is invalid.

24

EAGAIN

The O_NONBLOCK flag is set for the file descriptor, and the resource is temporarily unavailable.

25

ENXIO

The device does not exist.

26

EBADMSG

The data waiting to be read includes a control part.

28

EIO

A physical I/O error has occurred.

33

ESPIPE

The fildes parameter refers to a pipe or FIFO.

54

ECONNRESET

A read was attempted, but the connection was reset by its peer.

57

ENOTCONN

A read was attempted, but the socket is not connected.

60

ETIMEDOUT

A read was attempted, and the connection timed out.

63

EINTR

The read operation was interrupted by a signal

64

EISDIR

The fildes parameter refers to a directory.

81

EOVERFLOW

An attempt was made to read at or beyond the offset maximum associated with the file.

Remarks

The pread64 function returns the number of bytes of data transmitted from the file to the buffer.

The fildes parameter is a value returned by the open or creat function. When the file was opened, the access mode must have included either O_RDONLY or O_RDWR.

The data is read starting at the position specified by the off parameter. If any portion of the file prior to the end-of-file has not been written, the pread64 function returns bytes with value 0.

The pread64 function is equivalent to pread except that it handles files larger than 2 GB.

See Also