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NAME

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

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():
           _XOPEN_SOURCE >= 500
           || /* Since glibc 2.12: */ _POSIX_C_SOURCE >= 200809L

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 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.

NOTES

       On Linux, the underlying system  calls  were  renamed  in  kernel  2.6:
       pread()  became  pread64(), and pwrite() became pwrite64().  The system
       call numbers remained the same.  The glibc pread() and pwrite() wrapper
       functions transparently deal with the change.

SEE ALSO

       lseek(2), read(2), readv(2), write(2)

COLOPHON

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