pread, pwrite — read from or write to a file descriptor at a given offset
#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); |
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. The libc support (including emulation
on older kernels without the system calls) was added in glibc
2.1.
This page is part of release 2.79 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/.
|
Copyright (C) 1999 Joseph Samuel Myers. Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Since the Linux kernel and libraries are constantly changing, this manual page may be incorrect or out-of-date. The author(s) assume no responsibility for errors or omissions, or for damages resulting from the use of the information contained herein. The author(s) may not have taken the same level of care in the production of this manual, which is licensed free of charge, as they might when working professionally. Formatted or processed versions of this manual, if unaccompanied by the source, must acknowledge the copyright and authors of this work. |