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PREAD(2) Linux Programmer's Manual PREAD(2)
pread, pwrite - read from or write to a file descriptor at a given offset
#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
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.
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.
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).
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.
POSIX.1-2001.
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.
lseek(2), read(2), readv(2), write(2)
This page is part of release 3.32 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 2010-11-21 PREAD(2)
HTML rendering created 2010-12-03 by Michael Kerrisk, author of The Linux Programming Interface