PREAD

Section: Linux Programmer's Manual (2)
Updated: 2010-09-20
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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():

Since glibc 2.12:: _XOPEN_SOURCE >= 500 || _POSIX_C_SOURCE >= 200809L
Before glibc 2.12:: _XOPEN_SOURCE >= 500

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.

COLOPHON

This page is part of release 3.27 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/.

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Time: 19:49:19 GMT, April 27, 2011