PREAD(2)		   Linux Programmer's Manual		      PREAD(2)

NAME
       pread, pwrite - read from or write to a file descriptor at a given off‐
       set

SYNOPSIS
       #include <unistd.h>

       ssize_t pread(int fd, void *buf, size_t count, off_t offset);

       ssize_t pwrite(int fd, const void *buf, size_t count, off_t offset);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       pread(), pwrite():
	   Since glibc 2.12:
	       _XOPEN_SOURCE >= 500 || _POSIX_C_SOURCE >= 200809L
	   Before glibc 2.12:
	       _XOPEN_SOURCE >= 500

DESCRIPTION
       pread() reads up to count bytes from file descriptor fd at offset  off‐
       set  (from the start of the file) into the buffer starting at buf.  The
       file offset is not changed.

       pwrite() writes up to count bytes from the buffer starting  at  buf  to
       the  file  descriptor  fd  at  offset  offset.	The file offset is not
       changed.

       The file referenced by fd must be capable of seeking.

RETURN VALUE
       On success, the number of bytes read or written is returned (zero indi‐
       cates  that  nothing  was  written,  in the case of pwrite(), or end of
       file, in the case of pread()), or -1 on error, in which case  errno  is
       set to indicate the error.

ERRORS
       pread()	can  fail  and set errno to any error specified for read(2) or
       lseek(2).  pwrite() can fail and set errno to any error	specified  for
       write(2) or lseek(2).

VERSIONS
       The  pread()  and  pwrite() system calls were added to Linux in version
       2.1.60; the entries in the i386 system call table were added in 2.1.69.
       C  library support (including emulation using lseek(2) on older kernels
       without the system calls) was added in glibc 2.1.

CONFORMING TO
       POSIX.1-2001.

SEE ALSO
       lseek(2), read(2), write(2), feature_test_macros(7)

COLOPHON
       This page is part of release 3.27 of the Linux  man-pages  project.   A
       description  of	the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.

Linux				  2010-09-20			      PREAD(2)

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