PREAD (2)
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 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).
CONFORMING TO
HISTORY
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. The libc support (including emulation on older kernels
without the system calls) was added in glibc 2.1.
SEE ALSO
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