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



NAME
       pread, pwrite - read from or write to a file descriptor at a given offset

SYNOPSIS
       #define _XOPEN_SOURCE 500

       #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);

DESCRIPTION
       pread()  reads up to count bytes from file descriptor fd at offset offset (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 indicates 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  indi-
       cate 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 with-
       out 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 3.22 of the Linux man-pages project.  A description of the project,  and  informa-
       tion about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



Linux                             2008-12-03                          PREAD(2)